Using Video Analysis for Strategy

Video analysis can be used to evaluate sports performance and technique. We discuss many of the biomechanics aspects and tools used to do performance assessments right here on this website. Video analysis however can also be used to provide detailed game strategy and analysis of on field play.

We see these game strategy statistics all the time when we watch almost any sport on TV. How many shots did Kobe Bryant take and make. What percentage of first serves did Roger Federer get in and how many resulted in winning points. These statistics are fun for the viewer, but they are essential to the coach and player in refining their strategy.

Let's take an example from basketball, as we are currently watching the NBA playoffs. Any team coming up against the Orlando Magic this year will need to find a way to get past Dwight Howard, who was once again named defensive player of the year. The teams employ a coach or video analysts to watch every play that Howard makes. Every time he blocks a shot or an opponent manages to beat him and score. Using this information they can determine how best to play against him.

Below is video of some of Howard's best blocks of last season. Notice how often Dwight is alone and far away from an opposition player as he gets into position for the block. This may seem necessary in order to make the block, or as the Orlando Magic play a zone defense he may not have a specific man defensive assignment. Coaches or video analysts though would look at this video and may be able to create plays that take advantage of his position on the floor.

Of course a team also needs to play to its strength and similar video analysis of the coaches own team can be used to determine how they may take advantage of any opposition mistakes, close any gaps or change any patterns that may be obvious and strategies the best approach to take on an upcoming game or player.

To do Video Analysis of this sort properly you need to have some basic equipment.

• You will definitely need a video camera and to set that camera up so that you can see the whole game. This can be difficult in sports with large fields such as soccer or rugby.
• For larger fields you can use 2 video cameras, with each one focused on, one half of the field.
• A great advantage in well televised sports is that much of the video footage already exists. A recorded video of an NBA game will allow you to track most of the players on the court for most of the game.
• Some video analysis software is also recommended. This software can be the same as the software that you use for performance and technique analysis, but the software must allow you to tag events. Tagging events such as the first serve will allow you to go back and look at all the first serves in one place. This will enable some statistical analysis of the results of the serve and if you have software that allows it you can also analyze each serve for technique and performance.

The website http://www.thevideoanalyst.com/ has some great information on video analysis of this type and everything that you may need.

When working with a team or player combining this type of video analysis with biomechanics and technique analysis will provide excellent resources for performance improvements wherever they are needed.

Dribbling the Basketball While Running

Basketball as a sport can be made to look so easy. We watch Lebron James dribble the ball down the right side of the court while he surveys the positions of his team mates and the opposition. Suddenly he breaks left toward the basket, switching his dribble to his left hand, one more step and one more bounce then he switches back to the right hand as he elevates for the dunk.

Not once in this sequence does he look at the ball (until it is going through the hoop). As he does each movement, including side steps and head fakes, he keeps the ball bouncing slightly out in front and to the side, positioned ready for the next spectacular play.

Dribbling the ball is an essential part of basketball. A player that can dribble with confidence and control will have more options to attack the basket and get good looks to shoot a jump shot or attack the basket for a lay up or dunk.

We collected some video of a player running and dribbling the ball with his right hand, as well as some close up video of the players hand while he bounces the ball while standing.

We set up the video camera on the side of the court so we could watch the player run through the camera field of view. This allows us to see where he bounces the ball as he runs through. If the player ran toward the camera we would be unable to determine how far in front he pushes the ball.

The close up video of the hand will show a good example of how to bounce the ball in the dribble.

1. A correctly inflated basketball should bounce most of the way back up to your hand if you simply dropped it. You only need to push the ball down with enough force to get it back to your hand. Push too hard and the ball will bounce higher than expected and you may lose control.
2. Bounce the ball off your spread fingers. You do not want to push down with your palm. Allow your fingers to feel for the ball as it bounces up and then spread your fingers and push down on the ball for the next bounce. Push down by bending flexing (bending) your wrist.
3. Keep your head up surveying the court and position of your team mates and the opponents. You should do this whether you are running with the ball or simply standing still.
4. Keep your legs slightly bent and be ready to make your move. You do not want to be caught back on your heals as you are dribbling the ball as this makes it easier for an opponent to steal the ball. Be in a position ready to move.
5. Although we do not show this in the video, you should learn to dribble with both hands and on both sides of your body. This will allow you more options when driving toward the basket or preparing for a pass.

Now take a look at our player in the first part of the video as he runs at 3/4 speed while dribbling the ball. Dribbling while running fast can put your opponent off balance and create room for yourself and your team.

Here are a few tips to keep in mind when dribbling and running:

1. Once again, do not look down at the ball. You need to trust that the ball will bounce where you want it. This may be difficult at first but will come with practice. When running and dribbling it is even more important to keep your head up and see the court and be prepared to change direction quickly.
2. Bounce the ball far enough out in front of you so that you do not need to check your run to keep control of the ball. Many a fast break will come to nothing if you need to slow down to get control of the ball.
3. Bounce the ball out a little to the side. If you are dribbling with your right hand keep the ball a little outside and far enough in front of your right leg. If you bounce the ball directly in front of you then you will have more difficulty controlling it as you run. Of course if you are about to cut in toward the basket then you will need to bounce the ball in front of your body, but then you will also be turning your body or switching dribbling hands and will still be keeping ball slight outside your legs.
4. Once again use your fingers to bounce the ball and push it out in front of you. Do not use your palm as you are likely to lose control and probably the ball if you are running fast.

Practice will help you learn any new skill or get better at it. The more you practice the easier you will find the skill as your muscles and body learn what to expect and anticipates the limb movement and muscle action required.

We often say watch video of pros and of yourself and then practice with this in mind. Watching pros allows you to see how it should be done. Watching yourself ensures you know how you compare to these pros. Both are important. If you practiced all day but had no idea what you were doing wrong, you could teach your body to perform the skill incorrectly.

With video technology today there is no reason why you cannot easily assess your own performance. Take a look at previous articles in this website to find more tips on filming yourself or how to do specific skills.

Happy Holidays

Evaluating and Comparing your Broad Jump

The broadjump is a drill used to measure how far an athlete can jump from a standing position. The NFL has potential players perform this exercise during its annual combine, and uses the results as one of the many ways to evaluate the athletes' power. Below we have synchronized two athletes' broadjump trials. We've also slowed down the side-by-side video to help with the comparisons. And beneath the video window, we've included stillshot images of each athlete during key positions of their trials.


1. Loading Phase
During the loading phase, the athletes swing their arms back, in preparation to swing them forward. They will use this forward momentum to help them jump as far as possible. Also, notice their hips, knees, and ankles are all flexed (sometimes referred to as "triple flexion"). By flexing at these joints, the athletes are building up potential energy that will be released during the liftoff phase. From these two images, we see that the second subject has a slightly deeper knee bend than the first subject.




2. Liftoff Phase
During the liftoff phase, the subjects swing their arms forward and upward, and use this momentum to help propel their bodies forward. We see that the first subject extends his arms all the way, while the second subject has his arms flexed at the elbows. The second subject can definitely improve his form by extending his arms fully. Driving your arms forward as far as possible will allow you to use all the energy your arm swing can provide.

Also worth noting, their lower bodies also go through "triple extension" now (hips, knees, ankles), converting the potential energy into kinetic energy. We see that both subjects take off at about the same angle relative to the ground.




3. Maximum Height
In the pictures below, we see the key positions showing the subjects' centers of mass (COM) at their maximum heights, and at what distance from the start their maximum heights occurred. An athlete's COM during a jump follows a path similar to that of a ball flying through the air - in other words, it follows a parabolic arc. It will reach its highest point midway between the distance it is thrown. By driving your arms upward and forward you can get your COM higher and further forward. By then driving the arms down and bending your hips and knees forward at the top of the jump, you keep your COM elevated allowing you to gain added distance before touching down. Lifting your arms arms/knees and bending hips raises your COM. We see that the first subject reaches his maximum height at a further distance than the second subject.For the second subject, it's difficult to anticipate whether he will land closer or farther than the first subject though, as his maximum height is a few inches higher.

Both subject 1 and subject 2 have not remained fully extended through the peak of their jumps and have started to rotate for the landing. Subject 1 has begun to lift his chest, while subject 2 has already dropped his arms and brought his knees forward. Keeping yourself extended, as long as possible, through the peak height of your jump will allow you to jump further. A body position midway between that of subject 1 and 2 would probably be ideal.

At the peak of the jump it is now time to start rotating your body to get your legs out in front of you. The distance of the broadjump is measured where your toes land, so upon reaching the top of the jump, you should get your legs out in front of you. To make this happen, drive your arms downward and bend your hips and knees up toward your chest. Do not lean back as subject one has began to do; it is better to bring your hips and knees up to your chest.




4. Landing
In order to land safely and get the most distance out of the jump, our subjects flex their hips and extend their legs, landing on their heels with their toes pointed upwards. The second subject lands with his torso bent forward a bit more; but besides this and the placement of their arms, the subjects' landing techniques look quite similar.




5. Finish
The broadjump distances were measured from the subjects’ starting toe positions to their final toe positions. In order to absorb the shock of their landings, it’s important that the subjects bend their knees through impact. We see that the first subject doesn’t flex his knees as much as the second subject, and as a result ends up falling forward a bit at the end of the trial. This shouldn’t matter much though, as the jump distance has already been measured and the purpose of the drill isn’t to work on the landing. However, if someone was performing additional movements at the end of the broadjump (some training camps have the athletes do three consecutive broadjumps and measure the overall distance), it’s recommended to have more of a controlled landing at the end of each jump.




We hope you’ve enjoyed this article, and that you’re getting out there and filming great videos of yourselves and your athletes for detailed analysis!

Henry Gives France a Hand into The World Cup

Another week and another call for the use of video replay in sports.
This time from the football (soccer) World Cup qualifier between France and the Republic of Ireland.

Frances' William Gallas scores from an assist by team mate Thierry Henry. Replays and video evidence clearly show that Henry used his hand, intentionally, to control the ball before crossing it.

Watch the video below. Although I believe that Irish football commentary is often biased for their team, the commentary in this video is not biased. It is obvious that this goal should have been disallowed by the referee or the linesmen.



Henry admitted after the game that he had used his hand. I am not sure that any player with the desire to win this do or die World Cup qualification game would not have risked the same. I am sure he even expected the goal to be disallowed. Henry conned the referee and linesmen. Similar cases, particularly of players diving to win penalties, are prevalent in football at all levels and throughout the world. Players should never in my opinion deliberately try to con the referee. However I have no intention of passing judgement on Henry's character or that of any other professional athlete. This website is about video analysis, so once again we will harp back to a previous discussion on the use of technology and particularly video replay in sports.

In this particular instance we had some clear evidence of the hand ball from the TV footage. But again we need to point out that the evidence is not always that clear. See our previous post on video technology for refereeing. There have been numerous calls in soccer when the decision could have gone either way because of lack of clear video footage.

Watch this video of Wayne Rooney falling to win a penalty against Arsenal earlier this year. This decision is less obvious, was Rooney already falling or did the Arsenal goalkeeper touch his foot and bring him down? Was the ball close enough to be retrieved before going over the goal line? Even on watching the video it is a difficult decision to make.



The video technology in this case has let us down. A side on view of this same incident would have enabled us to better assess the position of the ball and the point at which Rooney begins to fall. We would also have been able to tell when Almunia, the Arsenal goalkeeper makes contact. So here is a decision that even with video replay remains controversial.

I believe that some amount of controversy actually brings excitement and emotion to the game. As a fan of a losing team, what better way to make yourself feel better than to suggest that the team would have won if the referee/player/coach/linesman hadn't cheated. In fact had Henry's goal for France been disallowed, Ireland would not have automatically won as many of the Irish believe (the score was 1-1 on aggregate before the goal went in), and may even have lost in the end anyway. Now just think of the great grudge match when France and Ireland meet again, even in sports other than soccer.

The problem is the blaming. With a referee in charge there are bound to be honest mistakes on occasion. Sometimes there may even be some blatant bias. The players too can make honest mistakes. A player falling over in the penalty box is not always trying to win a penalty, he may be trying to avoid injury.

Video replay technology can give increased accuracy to the decision. A referee is not always in the perfect position to make the most accurate call. Video from different angles can give the official added perspectives to help make his decision more accurate.

Video technology can remove all of this bias and simplify things. However it currently is not 100% accurate and controversial decisions will remain when the perfect camera angle is not available.

As technology progresses and even now with a good camera placement, such as those used in cricket and with the Hawk-Eye system for tennis, even more accurate decisions can be made.

It's time to bring in the video replay for all sports that rely on a referee or umpire to make a decision.

Table Tennis BackHand TopSpin

Table Tennis, which is sometimes known as "Ping Pong" in the USA is a dynamic sport requiring fast reactions from its players. A professional and skilled player is able to impart various types of spin to the ball, to keep their opponent on the defense and limit their options.

The backhand topspin shot is just one way to impart spin. Below is a great video describing the technique needed to hit a good shot both across the table and down the line.



This video is a fantastic example of using video footage to analyze motion. The camera is setup directly in front of the table tennis player so that we can see well how he changes his stance and hits the backhand topspin shot.

Table tennis is great exercise and fun to play. Learning a few different shots by watching and analyzing video, will help you enjoy the game even more.

Disguising your Baseball Pitch Like CC Sabathia

The Major League Baseball post season is nearing an end. The League Championship series are in full swing with two great match ups. The Los Angeles Dodgers are taking on the Philadelphia Phillies and the Los Angeles Angels have the formidable task of attempting to overcome the New York Yankees.

Baseball particularly in the post season is dominated by the pitching. Great batters are successful only around 30% of the times they come up to bat but great pitchers on the other hand can dominate and beat the batter 80% of the time. A great pitcher needs to be able to throw a variety of balls, so that he can beat any batter and can throw to the batters weakness.

• There are 3 pitch varieties, the fastball, breaking ball (slider or curve ball) and the change up.
• The pitcher must then be able to throw each of the 3 pitches listed above to hit 4 different targets: high inside and outside and low inside and outside.
• The pitcher also needs to understand the batter he is up against, his strengths and weaknesses. Is he left or right handed? Does he have an open or closed batting stance?What did the batter do on his previous at bat?
• Finally the pitcher also needs to throw pitches according to the pitch count. This is often called pitch strategy. The pitch strategy will change as the number of strikes and or balls change. For a detailed description of pitch strategy have a look at this article by Tom House.

In the first game of the American League Championship final between the Angels and Yankees , we watched CC Sabathia of the Yankees put in an excellent display of pitching. He pitched to all corners of the plate and varied his pitches with the pitch count and player.

Below is some video of Sabathia pitching strikes to the Oakland A's in August this year. Watch for the variety of his pitches, fastballs, breaking balls and change ups, as well as the numerous targets he hits, inside and outside, high and low, to both right and left handed batters.

Sabathia is one of the best in the MLB this year and his ability to pitch a variety of pitches is one of the main reasons for this.

However it is also important when throwing these different pitches that the player is able to disguise the type of pitch he is going to throw. If the pitch is well disguised it gives the batter less time to react to the pitch and reduces their chances of getting a hit.

Lets look at the video of Sabathia again. Notice that his action is always the same for every pitch, whether it is a fastball or a slider, whether he throws high or low. Focus on Sabathia only as you watch the video.

• Sabathia covers the ball with his glove at the start of every pitch.
• He rotates his shoulders back the same amount each time. He also lifts his front knee to the same height on every pitch.
• He seems to stride forward to almost the same position on each pitch.
• His arm comes through at the same speed and height for all his pitches. Most of the pitches he throws in the video above are in the 83-84 mph range, but the 2 faster pitches 88 and 97 mph look very similar to the others.
• His follow through for all pitches also looks the same. His head remains looking up and forward.
• He even completes the routine after the pitch in the same way by pulling up his shirt sleeve.

We all know from our experience that the video above is not the best for analyzing Sabathia's technique or timing. The best footage would be from the batters perspective, but from the angle we have, it certainly looks like each pitch is very similar. If the batter is able to read the pitchers mechanics and guess at the pitch to be thrown, he will have that little bit more time to modify his swing and get a hit. By throwing different pitches using the same technique and timing, Sabathia is able to delay the batters decision to swing and therefore is able to beat them more often.

The best technique for throwing all types of pitches is the same, there should be no need to vary your technique to throw a different type of pitch. To throw a curve ball, slider or any other type of pitch the variation is in the grip and in the final position and snap of the wrist, not the pitching mechanics.

To pitch like CC Sabathia, concentrate on the pitching mechanics. Fool the batter by showing him or her the same mechanics on every pitch. We will follow up with a video analysis of good pitching mechanics soon. In the mean time enjoy the post season and World Series. Keep an eye out for Sabathia and see if you can spot any variations in his mechanics with each pitch.

Wearable cameras for Sports Video Analysis

The Motion Capture technology company Vicon, announced yesterday that they had signed a license with Microsoft to develop a wearable camera based on the Microsoft SenseCam technology. The camera will automatically take pictures and I assume video for the wearer as they go about their daily activities.

Of course the camera has some immediate benefits to dementia and Alzheimers sufferers. The camera images will help these patients to create visual memories of activities during the day. The camera will also have application in patient monitoring, allowing Dr's to evaluate patients well being or compliance with a treatment protocol.

The articles on this website are about sports analysis though, and I believe that the Vicon Revue camera (the name for this new camera) will have benefits for sports performance too. Of course there are already cameras available that can be mounted to a helmet or some sports equipment and enable the sports activity to be viewed from a first person perspective.

Here is a great video using a helmet mounted video on a mountain bike.


So how can we use a wearable camera for analyzing sports performance. Here are a few suggestions that I think would be useful.

1. As we saw in the video above, the camera was mounted on top of the bikers helmet. A camera mounted on the helmet can help us to analyze head movement during the activity. Most sports require the head to be still during a particular motion. The head, with the skull and brain has a lot of weight for its size. Moving your head around during a sports performance can often throw you off balance.
2. The helmet mounted camera can also help analyze what we are looking at during the activity. For ball sports such as baseball, cricket, tennis and golf, the position of the head often determines how you will hit the ball. Lift your head too early during a golf swing and you may even miss the ball completely.
3. A wearable camera may also allow you to analyze your positioning in team sports. If you are a defender in soccer, the camera can assist in analyzing how close you were able to stay to your assigned mark.
4. A wearable camera may provide excellent feedback to a coach during a game. A player wearing the camera can provide the coach with important information about the oppositions positioning on the field.

Although video cameras are getting smaller everyday (the Vicon Revue is smaller and lighter than an ipod) , wearable cameras will probably need to get even smaller still before they can be used effectively in a competitive sporting arena or for that matter as a coaching tool. For the moment cameras can only be mounted on helmets or sports equipment and not all sports use suitable equipment.

Once cameras become small enough to be sewn into the badge of an athlete's jersey we may see many more application for first person, wearable, sports video analysis.

High Speed Sports Video on TV

We all already have or want that high definition plasma, LCD or even better, LED television. If you have watched sports on high definition TV, you know the difference immediately. The players are recognizable. No more asking who made that tackle or scored that goal?

Now a number of TV sports programs also show high speed replays, with the most prominent example being CBS Sports Swing Vision, which is used for CBS Golf coverage as well as Tennis and numerous other sports. We also see high speed video being used on TV and in sports to help make critical refereeing or umpiring decisions, such as the Hawk-Eye system for Tennis line calling and for the LBW decision in Cricket and high speed video replays for NFL challenge decisions.

Obviously there is a difference between high definition (or high resolution) and high speed video.
Normal TV images have up to 576 vertical lines of pixel data and the video is recorded at either 24 or 30 frames per second, depending on whether you are in Europe and Africa or in the Americas and Asia. The 576 lines describes the resolution or standard definition, while the 30 frames per second describes the speed of playback. Now your high definition television may have a resolution of 1080 progressive (1920x1080 or 2.07 MPixels) but the TV program you are watching is often recorded at the same frame rate as your standard definition TV, 24 or 30 frames per second. These days as more people have high definition TV's that can play back the higher frame rates, there are more sports broadcasts being filmed at 60 frames per second or even a little higher. This however is still not high speed video.

Therefore you can see that high definition television does not necessarily mean that we can always see slow motion replays of high speed motion. Special high speed cameras are needed to record broadcast quality high speed images such as those seen with swing vision.

High speed slow motion replays require cameras that record video data at 500, 1000 or 2000 frames per second and sometimes even higher. At the same time, they need to record with resolutions as high as 1080p, to retain their broadcast quality.

Swing Vision claims to record high speed footage with frame rates up to 40,000 frames per second. It is certainly possible for high speed cameras these days to record video at 1920x1080 pixel resolution at speeds of 2000 frames per second. To get higher speeds of capture broadcasters can trade in some of the resolution and for example record at 1280x720 pixel resolution (still HD) at 10,000 frames per second.

Below are 2 examples showing a HD video of surfing recorded at normal frame rate and played back in slow motion and a HD video of surfing recorded with a high frame rate and played back in slow motion.





If you pause the first video at any stage you will notice that the image goes a little out of focus. So although this video was filmed in HD, it was not filmed with a high frame rate. The fast motion of the surfer causes the paused video image to blur a little as her frequency of movement is faster than the frame rate of the camera.

The second video was recorded with the Typhoon HD4 high speed camera which can record video at 1280X1024 pixel resolution (1024 HD) at 1000 frames per second for full resolution. If you pause this video you will notice the clarity of the image. The surfer and wave frequency of movement is slower the camera frame rate.

We can see the difference between HD video of sport recorded at normal speed and high speed. The high speed recording allows for much more clarity in viewing high speed movement and therefore the chance to analyze performance in much more detail. In these surfing videos, you are probably thinking that the higher speed camera was not necessary to analyze the surfers movement as the clarity of the first video was more than enough. This is true but for higher speed movement such as the club during a golf swing, the higher frame rate can help identify those small improvements that can make a difference.

When capturing video of your own performance you may not be able to afford or for that matter need a high definition, high speed camera. Human movement, even fast human movement is predicted to have a maximum frequency of around 250 hertz. This suggests that even for the fastest human movement (not including equipment such as the golf club or tenis racket, which will move faster) 250 frames per second capture speed will be enough. But, the higher the frame rate you can get on your camera the more detail you will have to analyze in your video. There are numerous HD video cameras available and many of them can record at 60 frames per second and some even higher. To analyze your performance this is a great place to start.

Video Analysis of a Bench Press

This week University of Southern California football running back, Stafon Johnson, was bench pressing during training when the bar slipped out of his hands and landed on his throat causing severe laryngeal as well as neck injuries.

The bench press is a great exercise to build your pectoral (chest), triceps, biceps and deltoids (main shoulder) muscles. The exercise is used in training for many athletes in numerous sports, but especially in football. Johnson therefore would have bench pressed numerous times before and also had a coach or fellow athlete spotting him at the time of the accident. I am sure Johnson was using good technique and the accident was very unfortunate rather than a mistake on the athlete or trainers part. In most cases when a the bar slips during bench press it lands on the chest and causes much less damage. According to his doctor, Johnson should make a full recovery.

However it is important to understand that the use proper technique can help athletes avoid injuries such as tendon or muscle tears as well as build the muscles more effectively.

Below is a video of strongman Derek Poundstone from the USA bench pressing 500lb. Lets take a look at his technique.



Before we begin to analyze this video remember that when doing the bench press, always have a spotter, someone to help steady the bar or pull it up if you need it. We can see Derek's spotter watching carefully as he bench presses. It is also important to start with a low weight and test your ability before increasing the weight. very few athletes can bench press anywhere near 500 lbs. So start low, even if the bar is too low weight, you can always add more.

So here are some key points to note in the video above:

• Derek lays down under the bar and bends his knees drawing his feet up and pressing them into the floor. In doing this he creates a support base for his bench press and he is able to use his quadriceps (leg muscles on the front of his legs) to control his body and balance the bar. If he did not anchor his feet his body would be like a fulcrum with too much weight near the head and he would strain to balance the bar.
• Derek's spotter helps him to lift the bar off the supports and align the bar directly over his shoulders. He therefore can lower and push the bar straight down and up, with little angle. This will ensure that he works the appropriate muscles to their full extent and avoids injuries that may be caused by using muscle force to push at an angle that would put excess and inappropriate strain on the muscles or joints.
• He lowers the bar straight down to his chest, just below the nipples (the bottom of the yellow image on his shirt). Once again this ensures that his arms lower the bar straight down and push it straight back up.
• Finally Derek's spotter assists him in replacing the bar correctly. This is possibly where Stafon Johnson slipped and how the bar could have landed on his neck. You will see that Derek looks to make sure that the bar is properly supported on the hooks on both side of the support before relaxing and letting the bar go.

Before you start bench pressing, determine whether your goal is muscle mass or explosive power. You can build muscle mass with high weight and low repetitions or build explosive power by pressing a lower weight but increasing the number of repetitions. Whatever your goal is for doing the bench press, remember to use proper technique and spotter at all times.

The Straight Drive in Cricket

Batting in cricket is altogether different from batting in baseball in both objective and technique as well as the bat itself. In cricket the batter can hit or play at and miss as many of the balls bowled as he or she wants with a flat faced bat and scores by running between wickets or hitting the ball over the boundary. In baseball, it is 3 strikes and you are out and home runs or base hits, hit with a rounded bat, are the goal.

In both sport, professional bowlers or pitchers can deliver the ball at around 100 miles per hour and therefore timing and reaction are very important. In cricket though the batter can play a shot anywhere on the oval field, even behind him as long as he does not get caught or run out (I will not go into the rules of cricket but you can find them here). This means that in cricket there are a large variety of shots that can be played that require exceptional timing as well as perfect technique.

One of the classic and most eye catching shots in cricket is the straight drive. Most of the best cricket batters in the world such as Jacques Kallis and Ricky Ponting play this shot with ease and little effort.

Here is some video of Sachin Tendulkar, another cricket batting legend playing some straight drives off one of the fastest bowlers around, Brett Lee. The first shot is slightly mistimed and the ball angles off his bat, but the next 2 shots are perfect examples of a straight drive.



His timing and technique in the second shot is perfect and therefore requires little effort to transfer power and speed to the ball so that it races along the ground to the boundary and 4 more runs.

Let's analyze the video and break down his technique:

• Tendulkar starts his movement by stepping with his front foot toward where the ball will bounce on the pitch and lifting his bat. As the ball is coming toward him at around 145 km/hr, he has very little time to react and therefore must move toward the ball and plan the shot he will play at the same time.
• As bowling in cricket requires the ball to bounce, it can change direction and speed quite a bit after the bounce. Stepping forward to the area in which the ball will bounce allows the batter to get closer to the bounce and reduce the amount of movement that can occur after the bounce. This also allows the batter to get over the ball and prevent the shot from flying through the air and giving one of the fielders a chance to catch it.
• Tendulkar brings his bat down straight with the flat face of the bat directed at the ball. Angling the bat will force the ball off in the direction toward which the bat is angled and also increases the chances of catching the edge of the bat or missing the ball completely. Although batters do sometimes play shots by changing the angle of the bat, you will not play a good straight drive with an angled bat.
• Tendulkar connects with the ball around 1:21. By pausing the video you will see that his bat is alongside his front leg at the point of contact. His weight is also forward and over the front leg. He does this so that he can hit the ball directly toward the ground giving no chance for a catch. This timing also ensures that he has perfect balance and control over the shot.
• He keeps his head down looking at the ball being hit off his bat and continues to keep his head down as he begins his follow through. Just as in other sports (golf, rugby place kicking) this helps him to maintain his balance through the shot and once again to keep the ball from lifting into the air.
• Tendulkar then continues to follow through keeping the flat part of the bat facing in the direction he hit the ball and bringing his arms all the way above his head. This ensures that he hits straight and all the way through the ball.

The results of this perfect timing and technique are obvious as the ball flies off to the boundary and 4 more runs for Tendulkar.

The 2009 ICC Champions Trophy begins September 22 and the likes of Jacques Kallis and Ricky Ponting and Sachin Tendulkar will be showing off their batting prowess and often flawless technique from which we can learn.

The Skateboard Ollie

Skateboarding has taken off as a sport over the last decade and the tricks being performed are often incredible. To perfect these tricks skateboarders spend hours practicing and falling over and over again.

Video analysis is the perfect tool to learn how to do skateboard tricks. If you are learning a trick that someone else has already perfected you have the advantage of watching them do the trick and learning from them. You can also get video of yourself performing the trick and compare your technique to theirs.

Another benefit is that it is easy to setup a camera to get the best view for analyzing the video. Because most tricks are done over a defined area and in a specific direction, you can easily setup a camera to get the best field of view and angle to analyze the trick.

One of the more basic skateboarding tricks is the "Ollie" (jump). The Ollie is the basis for most aerial tricks in skateboarding and therefore it is important to learn how to do a great one.

Here is a really good video with a lesson on how to do an ollie. The video of the ollie itself is excellent because the camera is setup well and looking directly at the skateboard and movement and not at an angle.


The video gives a comprehensive description of how its done. We can get some other tips from analyzing the video more closely.

1. At the beginning of the ollie, the rider applies pressure to the tail of board. He does this to force the front of the board up into the air to start the movement. However if he only applied pressure to the tail he would simply fall off the back of the board. Watch how he also maintains his weight over his front foot so that the front of the board will only move up as he lifts and shifts his front foot.
2. Coming to the take off, the rider jumps up into the air but notice that he does not use his arms to jump. The idea with an ollie is to stay connected or at least close to your skateboard throughout the trick. If you use your arms to jump, you may jump too high above your board and end up having a long way to fall back onto your skateboard.
3. The rider in the video also lets us know that to make your ollie higher you "suck your knees up to your chest after you have jumped". This helps you to raise your center of mass and of course the height of your feet and therefore allows the board to lift higher into the air. Your center of mass is the center of all the limbs of your body, and is usually somewhere around your navel. You can move your center of mass by moving limbs. Therefore if you raise your arms you raise your center of mass. If you jump and lift your knees up higher you will also raise your center of mass.
4. Your center of mass is also important for maintaining your balance when landing the ollie. In the video note how the skaters right arm ends up behind him on the landing while his left arm is in front. He is balancing his center of mass over the center of the skateboard by opposite and equal balance of his arms. This does not mean that you need to have your right arm back and left arm forward when landing your ollie, but you should be aware that you need to balance your weight over the center of the skateboard (both forward and back as well as left and right) so that you do not fall off on landing.

Good luck with learning to do an ollie. You can try practicing your ollie first on grass or softer ground before moving to the cement. Remember to also wear a helmet, all the pros do.

Federer Practices his Between the Legs Shot!

If you were watching the US Open Men's Semifinal between Roger Federer and Novack Djokovic, you most likely saw Federer's incredible between the legs winner.

If not here it is:



Although we have video and some great angles, I am not sure that I am ready to analyze this shot. It is simply incredible. However, Federer said in the post match interview that he does sometimes practice the between the legs shot. We have also seen him use it before in match play, but never with such great power and precision.

Great players and athletes in any sport analyze and practice their technique all the time. They use video regularly to help them understand how to make improvements. Remember that all you need is a video camera and some basic understanding to analyze your own performances using video. Follow us here and look back through our previous posts to learn some tips and tricks for video analysis.

Video Analysis of Rugby Place Kicking

Great kicking in rugby can make the difference in close matches. In 1995 Joel Stransky kicked South Africa to the Rugby Union World Championships and in 2003 Jonny Wilkinson used his kicking boot to drive England to its first Rugby Union World Championships.

In Rugby Union in the past, penalty kicks of more than 50 meters were seldom, if ever attempted, but now the likes of Dan Carter and Francois Steyn are regularly scoring points with penalty kicks from as far out as 60 meters. The players may be be fitter and stronger now than ever before, but they also kick better and further because they study and improve their technique using video.

Lets take a look at some video of Dan Carter practising his kicks and break it down a bit:

• Dan is obviously a left footed kicker, so note that he approaches the ball at an angle (about 45 degrees from the target) from the right . You will notice that right footed kickers will approach at a similar angle from the left. The reason for this angled approach is to open up the hips and allow the hips and then the legs to swing through a larger arc and therefore create more power for the kick. We have talked about the Kinematic Sequence for the upper body before when discussing golf, tennis serves, baseball hitting and hockey slapshots. Kicking requires the same sequence but of course now we want to accelerate the hips, leg and then foot in sequence to kick the ball with power.
• Carter does not take too many steps before the kick ( 3 to be exact). Most good kickers will take fewer steps to eliminate the possibility of not being in exactly the right position to take the kick. If you attempt to run up further there is a chance you will take a small or big step along the way and be out of position for the kick.
• Dan plants his right foot just adjacent (next to the ball). If he placed this standing leg behind the ball it would force his kicking foot further under the ball forcing the ball higher in to the air but getting less distance. Alternatively if he overran the ball, placing his support leg past the ball he would not be able to swing his leg through and get under the ball sufficiently to get the distance required.
• His hips, leg and foot kick through the ball in sequence. If you pause the video you will notice how his hips rotate through toward the target first and his knee is left bent behind. The knee then straightens out and brings the foot through the ball toward the target.
• He keeps his head down over the ball as he kicks. Keeping your head down looking at the ball ensures that you are balanced for the kick and that you strike the ball cleanly.
• Finally he follows through with his hips and kicking leg. You will need to pause the video just after the kick to see this clearly. Note also that his head stays down through the follow through, once again ensuring that he maintains his balance.

In the video we can also see that Carter rolls over his support ankle (right foot) during the follow through. This happens because of his angle of approach toward the ball, which I have suggested allows him to get a bigger swing at the ball. Although this looks dangerous , the roll is forced by his follow through when most of his weight has been lifted from the support leg. You will see that some kickers look like their support leg is lifting into the air, rather than rolling, with the force of the follow through and as their weight is lifted from this leg.

This weekend South Africa takes on New Zealand in a match that could be crucial in deciding the 2009 Tri-Nations champions. We will see Dan Carter and Francois Steyn in action and most likely kicking some big goals. I am originally from South Africa so I will just say it.
Go Bokke!

How Accurate is the Hawk-Eye System for Tennis Line Calls

The US Open Tennis 2009 is in full swing. Once again the likes of Federer, Nadal and Murray are playing well and the men's championships looks set for an exciting second week.
We know and have seen how video analysis can be used to analyze a tennis players performance, but it can also be used in real time or almost real time to track the ball and even make close line calls. Of course I am talking about the "Shot Spot" or Hawk-Eye system.

If you have watched any Major Tennis since 2006, you will know exactly what Hawk-Eye is. The Hawk-Eye is used to make decisions on line calls that are challenged by the tennis player. Each player (or team if playing doubles) can challenge a line call on any point. They get a maximum of 2 incorrect challenges each set. If the set goes to a tie break an extra challenge is allowed. Basically the Hawk-Eye challenge enables the tennis players to use technology to challenge line calls they think are incorrect.

The technology being used by the Hawk-Eye system is Video Analysis. Here is how it works.

1. Multiple cameras are placed around the court and players. These cameras are usually placed high up, so that there is less chance that a player will be blocking the ball from the camera view.
2. Multiple cameras are used to ensure accuracy of tracking the ball and to account for possible occlusion (the ball being hidden from the camera view by the players body...)
3. The system uses at least 4 high speed video cameras, with a capture rate presumed to be 500 frames per second.
4. The camera position is calibrated to determine its position in space and relative to the other cameras in the system. The lines on the court are also used in calibration and to compensate for any camera movement.
5. The center of the ball is tracked in 2D by each camera. The ball therefore is like a reflective marker or point on the body. Using the information from all the cameras, the Hawk-Eye system then triangulates the 3D position of the ball.
6. This process is done for each captured frame so that a trajectory of the ball can be created and then overlayed on an animated background containing the lines of the tennis court.
7. Finally the skid and compression of the ball is measured by examining the position and trajectory of the ball prior to the bounce and its position and trajectory after the bounce. In this way they can determine how long the ball was on the ground and how it skidded over the ground.
8. The Hawk-Eye system is said to have an accuracy of 3.6 mm.

I believe that the use of video technology in this way is great for the sport of tennis and for the players piece of mind as well as spectator enjoyment. However we have seen a number of controversial calls with the Hawk-Eye system. Take a look at video of 2 big ones here.

In this first video we see a very tight call for Mikhail Youzhny over Rafael Nadal at Dubai in 2007.


This second video is from the Wimbledon final in 2007. Rafael Nadal benefiting from a very close one over Roger Federer.


In both cases we would have to say that the ball likely looked out to the lines judge who made the call. In both cases the player is most likely only challenging the call because it is a crucial point (Yozhny vs Nadal - Set Point, Nadal vs Federer - Break point). The Hawk-Eye system suggests that in both cases these calls were measured as being 1mm IN, meaning the ball was 1mm from being out.

Have a look what the manufacturers of Hawk-Eye have to say about these two controversial calls at here.

Could Hawk-Eye have been wrong in either or both of these calls and what does it mean that it is 2-3 mm accurate but can suggest that the ball was in by only 1mm?

Here are some points that may effect the accuracy of the system.

1. The camera capture rate of 500 frames per second may be too slow for the hard hitting tennis game of today. Andy Roddick has recorded a fastest serve at 155 mph and ground strokes are often hit with a similar speed. Assuming a capture speed of 500 frames per second or 1 frame every 0.002 seconds, the ball will have moved about 139 mm for every video frame. This may not be sufficient data to determine the position of the ball to within 1 mm.
2. The more cameras that are used the better the chance of tracking the ball and the higher the accuracy. However there are possibilities of occlusion by players, tennis rackets and the net, which will lead to reduced accuracy.
3. High speed video capture also needs excellent lighting. We have discussed the importance of lighting for high speed capture in a previous post . Therefore the system will work best under a roof with artificial bright lighting and will possibly have a problem tracking the ball outdoors, particularly when there is cloud cover or as it gets later into the evening.
4. Assuming everything is perfect for capture, the center of the ball has to be identified as accurately as possible too. If a camera sees the ball at a funny angle or partly occluded the center may not be correctly defined by this one camera and the position of the ball will be inaccurate.
5. The skid and compression of the ball is being estimated and extrapolated based on the trajectory of the ball before and after the bounce. Any inaccuracies in tracking the position and flight of the ball will become larger during an extrapolation (estimation of the movement).

The Hawk-Eye system may not be perfect but it is definitely a step up from the eyeball view of a line judge, particularly when the ball is moving at high speed. We believe Hawk-Eye has improved the line calls in Tennis and this is great for the players and spectators alike. However it still leaves room to debate exciting points and close matches. Enjoy the US Open Tennis and hopefully we will not see any controversial Hawk-Eye calls.

Which Sport Has Bigger Hits, Rugby or Football?

Most of us who have watched or played both Rugby and Football know that the tackles are often hard and dangerous. We also regularly try to compare the hits. Is it worse to be hit hard in a rugby tackle or in football?

On the football field the force of the hits look more spectacular. Players can be tackled in numerous ways, even with the head. The aim of the tackle is to stop forward progression and bring the player down to stop the play. In a great tackle the player is also trying to make the receiver or ball handler fumble. In getting hit there is the added concern for the wide receivers who have to watch the ball and often jump for the catch. They can get hit while still in the air and without expecting it. Of course the athletes are also wearing padding and helmets and therefore have some form of protection.

In rugby the tackle is meant to stop forward progress of the ball handler and to simultaneously bring him to the ground so that he can not pass the rugby ball out quickly. Tackles in rugby often need to be lower (around the knees or waist) to ensure the player goes down. The tackle also does not stop play and players need to be ready to get up and tackle again almost immediately. Of course in rugby there are no helmets or pads, so there is little protections for a big hit.

OK so which tackle is harder on the player? We could measure the speed of the players as they run into each other and weight that against the benefits of the padding. In the end both sports have big hits and there are too many differences in the rules of the game and the equipment to truly compare them. So take a look at these two videos, the first of big hits in rugby and the second of some big hits in football and make up your own mind.





Hope you enjoyed watching those big hits. The Tri-Nations Rugby Tournament between South Africa, Australia and New Zealand is nearing an end as South Africa continue to dominate World Rugby. Meanwhile the NFL preseason is in full swing and starts proper in mid September. So enjoy the big hits from the upcoming Tri-Nations games and NFL season.

Let us know which sport you think has the bigger hits and why.

Performance Analysis of Surfing: Rodeo Clown Flip

Anyone who has seen a surfer or skateboarder pull off a flying aerial move is amazed that a human can do such an incredible trick. Although we are all completely dumbstruck by the performance of these maneuvers, these sports often have an unfair reputation of not being truly professional. We often consider these athletes to simply be kids who have spent too much time playing around on the beach.

Surfing and Skateboarding are no longer sports dominated by athletes with talent only. These professional athletes spend many hours training. Professional surfers now spend almost as much time out of the surf, working out (often with trainers) on balance balls, with weights, and in the gym and swimming pool. They do thorough warm up sessions before going out to compete and often also have cool down routines for after a surf.

The use of scientific analysis in surfing has been long in coming. There are a number of reasons for this and I won't give you a history of soul surfing, but the main reason is the difficulty of doing any physiological or biomechanics testing on a surfer. Because surfers do their sport in water and shifting, changing waves (size, direction, steepness...), it is very difficult to test them in the same conditions and obtain relevant scientific results.

Recently, for the first time a team of scientists joined some professional surfers in the Mentawais and recorded their paddle speed, surfing speed and heart-rate during surfing sessions. They also took blood samples to monitor lactic acid build-up and hydration data. These scientists were able to provide the surfers with some physiological and performance data which will surely help them to train better for competition.

Using video to analyze surfing is another way in which these athletes and other non-professional surfers could improve their performance. The professional surfers get lots of video of their performances from all different angles and we hope they use this information to make improvements. Of course, because of the changing waves and the 3 dimensional nature of surfing (moving up and down, forward and sideways), it is difficult to make comparisons with video.

As we looked through some of the video from the surfing trip to the Mentawais, we found one of Jordy Smith of South Africa, performing a Rodeo Clown Flip. We won't try to describe the move here. At about the same time at a competition in the Maldives, an American surfer, Patrick Gudauskus was completeing the first ever rodeo clown in competition. We have decided to look at both these videos and compare their performances. Jordy's wave is the first video and then Pat's wave is the first part of the second video.





Once you get over being completely amazed that surfers can do such things on a wave, take a closer look.

The first thing you will notice is that Jordy is on a much bigger wave than Pat and this can make comparison difficult. We can still look at the technique though and we will do this in stages.

1. The Setup: Jordy launches into his rodeo clown with his board facing almost vertically up at the sky, while Pat's board is about 30 degrees from the vertical when he launches. This may be because of the size of the wave. However, what is obvious is how this affects the height of the flip. Jordy's vertical entry helps project him higher into the air.
2. The Take Off: Here both Jordy and Pat transfer their weight onto their back foot. This helps them launch the board out of the water, bring the board up to their hands for the grab and creates the rotation by pushing on the back of the board.
3. The Grab and Spin: Once again they both use a similar technique here. They both grab the board quickly once they are in the air and begin their rotation. Some of their rotation has come from the back foot pushing on the board but once they are in the air they both use their heads to complete the spin. Watch how they both turn their heads to their left (the direction of spin) . If they did not use their heads to turn they would not be able to complete the spin.
4. The Top of the Flip: As they spin around both surfers actually travel upward to their high point. The high point of the flip is determined by the surfers maximum height above the wave. It is obvious here that Jordy is much higher than Pat throughout the flip. At the top, Jordy's body and board are well above the wave (we can see sky and clouds between him and the wave). Pat's board and body are at just about the height of the wave. Although in this case it does look like Jordy is much higher we need to clarify this by pointing out that Jordy is on a bigger wave (this is not controlled by the surfer) and the camera angle filming these two flips is not the same and therefore the camera angle used to film Jordy's flip may be making it look much higher than it was.
5. The Landing: The landing of course is dependent on all the other factors that occurred before, including the take off, spin and height. Jordy has rotated further and is still above the wave as he prepares to land. He therefore needs to stretch out his legs to find his landing and ride out of it. Pat, on the other hand has not been able to rotate as far, because he did not get the same height above the wave. He is forced to land low down, but by landing with knees bent and hands still on the board he too is able to ride out.
   

So both of these flips were spectacular and although they looked different they were actually performed with similar techniques and there is a lot to learn by analyzing the videos.

Unfortunately, those of us who surf for fun and do not have sponsors, do not have too many opportunities to see ourselves in action. You can however set up a camera on a beach or get someone to film you from the beach. Try to get video looking straight out at the wave from the beach. It is difficult to analyze your performance when studying video that was filmed at an angle to the wave. It is also useful to have some sort of calibration scale that can be used to measure height (as we did in a previous post on Measuring Jump Height). Of course if you can get more than one camera setup you can really take a look at your technique from multiple views, which makes sense for a sport such as surfing.

We love to hear your comments or suggestions. Let us know what you think or what you want to see posted.

Andy Murray's Tennis Serve

Last week, Rafael Nadal won the 2009 BNP Paribas Tennis Tournament at Indian Wells, California, defeating Andy Murray easily in the final.

As we watched the tournament, we heard frequent discussions of Murray's second serve, and that if he could develop a better second serve he would be almost unstoppable. Of course, he was almost unstoppable at Indian Wells, but did lose badly in the final, mostly because of poor serving. In that final match against Nadal, he lost his service games four times and won only 6 of 16 (38%) of his 2nd serve points. Let's take nothing away from Nadal though; he has the best return game in tennis, possibly the best ever.

All tennis players, including beginners, know the importance of the serve. A good serve can result in easy points and puts pressure on an opponent. The first and second serves in tennis usually have different goals. With your first serve, you want to win the point with an ace, service winner, or at least put your opponent in a defensive position for the next shot. The first serve is generally flat and fast, and you can take more risk, knowing you have an attempt at a 2nd serve if you need it. The second serve is your backup safety. Your priority is to get the second serve in and start the point. If you miss the second serve, you will double fault and give your opponent a free point. Most tennis players put a lot more spin on the second serve, but this tends to reduce the speed of the serve.

Because of the slower pace, the second serve often gives the receiver plenty of time to get into position to hit an aggressive return. However, if you can make your second serve look similar to your first serve, at least in terms of the service motion, you can make it difficult for the receiver to predict the speed (and type of spin) of the serve, and you may retain a significant advantage, even as you serve slower and with more control.


We found some video of Andy Murray's first serve and decided to look at it from a biomechanics point of view. This video is set up very well for video analysis. The camera is set up along the baseline, which allows us to get a side-on view of Andy during his serve. We can also see the complete service motion in the video, including the racquet head, and can see the racquet make contact with the ball. It would have been great if we could've seen the complete ball toss (the ball goes out of the top of the screen) and if the camera had been stable and mounted on a tripod; but in general, this is good video sports analysis footage.



The power in the tennis serve, like many throwing or hitting sports (baseball hitting and pitching, football throw, and golf) is created by a chain of events. Each part of the body loads up with energy and transfers its energy to the next link in the chain. The timing of this energy transfer is critical to creating racquet head speed and therefore a good, fast serve.

In Andy's serve, we see how he starts with his knee bend as he throws the ball up. You may also notice that as he bends his knees his hips turn away from the court. He then transfers this energy now stored in his hips by bringing his back foot up to his front foot and rotating his hips into the court. Once again notice that as he rotates his hips back into the court, his shoulders now rotate away. This counter rotation in both hips and then shoulders creates the potential for racket head speed; Andy is coiled up and ready to explode his racket toward the ball.

As he does this, he releases the potential energy, rotates his shoulders back into the court, and throws his racket at the ball. All these energy transfers add up to create the speed with which he will hit his serve. If his timing is off, his speed will not be as high.

The ball toss is, of course, just as important. If you do not throw the ball consistently, it will be very diffcult to perfect the timing of your kinetic chain (described above). Andy's ball toss is high and a falls about a foot inside the court. If you want to hit a good hard serve, the ball needs to be in front of you, so that your body and racquet are moving forward when the ball is struck. If the ball toss is directly above your head, it is much more difficult to get theball moving forward with as much pace.

Ok, so Andy has a great first serve, and we can see that here. It is his second serve that the commentators were discussing. Unfortunately, we were unable to find any good footage of his second serve to compare it to his first serve. We are sure his coach is working hard on improving his kinetic chain sequence and timing to make it more difficult for his opponents to read his second serve.

Please post comments and let us know what you think, or whether you have any questions or suggestions. We would be delighted to hear from you.

Video Analysis of the Basketball Free Throw

We know why you visit our blog, to learn how to capture and analyze sports performance. Today we present our first videos and some biomechanical analysis done with free video analysis software.

Before we begin, we want to remind you that our intention is to show you the tools you can use for the video analysis of sports. We are biomedical engineers who have done research and work in sports performance analysis, but no one can be an expert on all sports. Therefore, although our biomechanical analysis is correct, our coaching tips (which we will minimize) should be evaluated with a professional coach in the appropriate sport, and must be evaluated on an athlete-by-athlete basis.

With the NCAA basketball tournaments about to begin and the regular season of the NBA about to end, we know many of you are spending a lot of time either watching or playing basketball. In honor of March Madness, our videos this week are of a basketball free throw. We have video of two subjects with very different techniques shooting a free throw. We have set up our camera on the side of the subject, as we wanted to evaluate the subjects ball release angle.
The two videos can be seen below. Notice that both the free throw shooters are right-handed therefore it would have been more appropriate for us to shoot the video from the other side of the court, so that we would have a clear view of the right arm. However, in this case, lighting conditions and other background interference meant that shooting from the left side of the athlete would result in a sharper image to analyse. We were, however, lucky that in both videos we can see enough of the shooting arm and ball to evaluate the release angle that we are interested in.





With these two independent videos there is already so much we can analyze. We can see that Subject 1 jumps quite high off the ground for his free throw and also falls forward, while Subject 2 goes up on his toes. As the camera was set up in almost the same position, we can immediately notice that Subject 2 is quite a bit taller than Subject 1 and we can take that into account in our assessment. Subject 1 is jumping in order to gain more height on his free throw. This is causing the ball to come out of his hand at a flatter angle.

A feature of many free video analysis software is that we can compare two subjects side by side. When comparing 2 subjects, it is important to also synchronize the video to a specific event. In our comparison video below, we have synchronized the two subjects' free throws at the point of ball release. We need to synchronize video for comparison because not all videos are the same length, as some subjects may take longer to shoot their free throw than others. If we tried to analyze two videos of free throws that were not synchronized, we would have a very difficult time ensuring that we could see both subjects releasing the ball at the same time. The free video analysis software we used allows us to synchronize side by side video, but not to save it out as an avi. We therefore used a well-known video analysis software to create the synchronized view you see below:



If you are a basketball coach, you can probably see a few things that can be improved for both

Subject 1 and Subject 2. Please send us your comments or coaching tips if you have suggestions.
We however are going to suggest some improvements for subject 1 based on a little bit more video analysis we did with a free video analysis software package.





Here are two freeze frame images of Subject 1 (top) and Subject 2. Using free video analysis software, we have calculated the angle of release for both subjects, and zoomed in on their arms and the ball at this release point. Subject 1 released the ball at 48 degrees to horizontal while Subject 2 released the ball at 79 degrees to the horizontal.

Now for some basic physics. The diameter of the basketball rim should be exactly twice the diameter of the basketball. In other words, two basketballs can fit through the hoop at the same time (if everything is perfect and there is no net). During a free throw or any basketball shot from the outer court, we are throwing the ball on an arc. The ball needs to move forward as well as up (for most of us) to get it into the net. The ball can either move on a flatter arc (Subject 1) or on a steeper arc (Subject 2). On a flatter arc the ball will not go as high but will move forward further and quicker; on a steeper arc, the ball will go higher and not as far. This means a free throw on a steeper arc will come down straighter and take advantage of the size of the basketball rim, while a flatter free throw will need to be far more accurate as a ball moving forward is more likely to hit the rim.

Subject 1 should try to put his free throw on a higher arc to take advantage of the physics described above. He can see immediately from this video analysis that his free throw is at a 30 degree flatter angle at release than Subject 2 and while practicing his free throws, should concentrate on releasing the ball on a higher angle. Once Subject 1 has some time to practice, we will get another video of him and see how he has improved.

Hope you enjoyed this first full Video Analysis. Remember that you too can do this type of in-depth analysis. All you need is a video camera and a little understanding. Follow us to get more tips, tricks, and understanding in using your video camera to analyze different sports.

We are happy to answer any questions or hear from you, please leave us a comment.

Video Analysis of Sports 101

Welcome to the Video Analysis of Sports blog. As this is our first article, we will take this opportunity to introduce ourselves.

We (Dennis and Dudley) have a combined 20 years experience in motion capture and biomechanics with a special interest in sports performance and injury prevention. Through our consulting company Sadaka, LLC http://www.sadakallc.com ,we offer services to sports professionals, sports equipment manufacturers, hospitals and motion analysis software and hardware companies. Some of our past clients include Titleist, FootJoy, Warrior Hockey, National Pitching Association, NASA, Shriners Childrens Hospital and Vicon Motion Systems.

Video analysis of sports performance is often the domain of professional athletes and large companies or research institutions. This analysis is done with expensive 3D video camera equipment and complicated software to ensure high speeds and accuracy. However there are some basic techniques that can be used by any individual to evaluate their own performance and get great results using a simple digital video camera and a little understanding of biomechanics. The video camera will require a small cost (we will discuss what makes a good camera in a future posting), but we will supply you with much of the biomechanics understanding for free on this blog.

Reviewing video clips can be a great way to provide coaching feedback to players, as well as a means to emulate one's favorite athletes. Whether you're a professional all-star, high school athlete, or weekend warrior, seeing yourself from a different perspective can help improve your performance and/or minimize your chances of injury.

So in this first posting, we'll start right at the beginning and describe what features make a sports clip suitable for video analysis of an individual, and what you can do to ensure the clips you film will meet those requirements. Future postings will demonstrate the various levels of analysis that can be performed on suitable videos, using a range of available software, from basic free software to detailed 3D analysis.

What makes a good sports clip?
A good sports clip of an individual shows the athlete's full range of motion (ROM) during an action, with the camera positioned such that angles can be accurately calculated (this will be discussed in more detail later). Filming the athlete's ROM can be accomplished by simply zooming out or moving the camera backwards until all the desired features are in the viewer. In general, it's recommended to have the camera as close to the athlete as possible and still capture the entire ROM, as this will make the most use of the camera sensor's resolution. For example, if we were to capture a basketball player dunking the ball we would want to ensure that our camera can see the complete action from take off until the player puts the ball in the net. Our camera would therefore need to see the ground at the take off point as well as some space above the rim of the the net.

Another important factor in obtaining a great sports clip is to make sure that your camera is stationary. There are some motion capture software available that can handle a moving camera, but for now we suggest that the camera is mounted on a tripod and is not moved while the video clip is being filmed. This means that you should ensure the full ROM (described above) can be captured in this one shot.

How you can film useful footage:
Camera placement
In general, most sports clips we watch on tv are best suited for analyzing strategy and teamwork because they provide an overall picture of many or all of the competitors and the playing field. However, when it comes to analyzing an individual's performance or technique, it's not only important to focus the camera on the single athlete, but the angle we film from must also be taken into account. It's best to use "orthogonal angles", meaning the camera is directly in front of, behind, or to the side of the athlete. Golf coverage usually does a nice job of this, providing shots of the golfer either "face-on" or "down-the-line". Here's a great face-on view of Tiger Woods' swing:



And here is a down-the-line shot of his swing:



Notice these cameras are level with the golfer; they're not filmed at an upward or downward angle, meaning it's possible to accurately calculate some angles, if that's what is desired from the analysis.

Background/contrast
Although the above clip is a beautiful view of Tiger's swing, the footage could have been improved by having him wear clothes that were a different color from the background. Black clothing with a black background can make it difficult to accurately evaluate the amount of hip and shoulder rotation - two commonly analyzed characteristics of a golf swing. Not that having a solid black background is a bad thing though; on the contrary, if you can manage to film your athlete with a solid-colored background, you are well on your way to filming some nice footage for analysis.

Lighting
As is true with taking most photos, it's ideal to position the camera and athlete such that the light source (e.g., the sun) is behind the camera and illuminates the athlete. This will provide a crisp view of the athlete, and will allow you to use a more open setting on the camera's aperture.

Now that you're up to speed on the basics of filming great video for analysis, grab your video camera and start practicing! Follow our regular blog postings, and see how you can create your own analyses of your videos, using a variety of software packages.

-Dennis Ho