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.

Replay Technology Will NOT make 100% Correct Calls

More blown calls in a major sporting event. This time in the 2nd game of the Major League Baseball World Series, between the New York Yankees and the Philadelphia Phillies. Chase Utley of the Phillies was called out at first base, when video evidence suggested he had touched the base before the ball hit Mark Teixeira’s glove. In the same game Ryan Howard was judged to have caught out Johnny Damon, when the ball looked to bounce before hitting his glove. There have been a number of poor calls in this seasons MLB playoffs once again, and blown calls are happening in numerous other sports, including soccer and tennis.

The technology of high definition and high speed video of today can easily eliminate many of these blown calls. Sure there is the argument that using video replay can slow down the game. In baseball in particular this would be truly frustrating, but we would I think all prefer to see the right call made most of the time, particularly in big games such as the World Series.

Cricket is a great example of where camera technology is used to good effect. The cameras are setup side on to the crease (batters line) and can see both the wickets and the crease. In most cases just this one camera would be enough to determine the position of the batter as well as whether the wickets bails had been dislodged. If the umpire on the field is unsure of a run out situation, he will refer the decision to the camera technology, or the 3rd umpire, who will make a definitive decision after reviewing the video footage.

Although we definitely support the use of video analysis to assist umpires and referees, it is important that everyone; umpires, athletes and fans understand that even with video analysis a call can not be 100% correct every time.
Video footage cannot always capture the event from the correct angle or the video cannot be slowed down sufficiently to determine some calls. The fact is that the video footage may not show enough evidence to support or over rule a call.

Fans in particular make the mistake of believing that video evidence will always be able to determine whether a call is correct. Unfortunately this is not the case.
If the camera reviewing a line call or judgement does not have a direct view, then the video image may not help to determine the accuracy of the umpire's call. When close calls are viewed from an angle given by a television camera, they can sometimes give misleading evidence of the accuracy of the call. This can be particularly problematic for example, when using one camera angle to determine whether a base runner has been thrown out. The base runner is running between the bases and the camera could be setup at a good angle to view when the runner touches the base. However, and here is the problem, the ball may be thrown in to the fielder from anywhere on the field (this cannot be determined in advance), therefore the camera setup to view the runner may not be in the best position to accurately determine when the fielder caught the ball and it will be possible for incorrect judgements to be made. If on the other hand we have a great view of the fielders glove and ball, we may have the incorrect perspective of the base runner and when he touches the base.

Of course these 2 situations did not take place in the 2nd game of the MLB World Series, but they also cannot be discounted.

Take a look at the 2 photographs below.


In the above pic we have the view from one camera and shoe looks like it is on the edge of the mat.
Now lets take a look from a second camera with a better view of the edge of the mat and the shoe.

Of course it is pretty obvious from this camera angle that the shoe is just short of touching the mat.
From this we can see that the incorrect camera angle could result in an incorrect call.

The problem of incorrect camera angle could be solved by having multiple cameras, all synchronized with a time source and calibrated so that the 3D position of the ball can be determined. This is how the Hawk-Eye system for Cricket and the Tennis challenge system works. Beside the fact that this type of technology requires numerous cameras, can be very expensive and requires processing time before a decision can be made, it too can suffer from inaccuracies when the ball or target being tracked is hidden from the view of a number of cameras. This can often be the case when their are numerous players on the field, or the lighting is not ideal.

So we know that video analysis of umpiring and refereeing decisions are not 100% accurate. In fact the Hawk-Eye system claims they have an accuracy of 3.6mm. This means that the ball can miss the line by 3.6mm in Tennis and still be called in by the system. In NFL football when a call is challenged and a review takes place, often the result suggests that there is insufficient evidence and the call on the field cannot be over ruled. This insufficient evidence occurs because the camera cannot get the best view of the ball and its position because of the scrum of players or a camera angle that is not optimal.

The umpire or referee has a distinct disadvantage to technology. He or she only gets one chance to get it right. If they fail to get into the best position, have the best view of the play, find the best perspective to catch all the action and happen to blink at the critical point, they could easily make the wrong call.
The camera even with the possible errors in perspective or lighting and the small errors with 3D tracking , can capture high resolution and high speed footage and replay it over and over again.
This advantage will ensure that technology will get the call right more often than even the best and luckiest umpires and referees and should be used whenever an umpire is unsure of the call to be made.

A final thought. While we wait for technology to be used, we should remember that even video footage could result in incorrect decisions. There will always be some statistical error, only a lessor error than those made by human umpires. Fortunately with technology, line calls can not be biased by emotion but only based on whatever video footage is available. With this technology even the teams we support will catch a few breaks in the long run.

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.

Improving your Cycling Efficiency with Video Analysis

The Tour de France is the ultimate in road cycling competition. Covering 3500 kilometers (2187 Miles) over 22 days, the event tests the cyclists mental and physical strength. To complete in this grueling endurance test, the athletes need to be in peak fitness, but they also need to ensure their technique is as efficient as possible. Energy can be preserved, injuries prevented and more power created with good technique.

The best way to evaluate your cycling form is with a few appropriately positioned video cameras. Although you may encounter flats, up hills and down hills on your bike ride, the general position for cycling is the same and therefore you can benefit greatly by improving the efficiency of your cycling power stroke. Although there may be various inclines and flat sections, your position during the ride is generally constant, and therefore you can benefit greatly by improving the efficiency of the cycling power stroke. The power stroke is the cycling pedal stroke including the push down and pull up of the pedal.

Assume you are sitting on the saddle of your bike with your upper body still (as it should be). The power required to turn the pedals over comes from the muscles in your hips, thighs and calves. This power is transmitted to the pedals, and from there drives the cogs and so on, turning the rear wheel.

Now for some basic physics. In order to push down on the pedal or pull the pedal up with the greatest force and the most efficiency, you will want your muscles to generate a force that pushes or pulls directly down or up on the pedal (depending on whether you are in the down stroke or up stroke of the pedal motion). Your hips, knees, and feet all need to be aligned correctly to produce a purely vertical force on the pedal.




In the image above we have the side view of a cyclist. The cyclist cannot use his thigh muscles to push directly down on the pedal but we can see that his knee is directly above the middle of the pedal which will allow him to push down efficiently as he straightens his knee. The force (red line) from his thigh muscles will be transmitted along with the force from the calves to the pedal. If his knee was in front of the pedal he would be wasting energy pushing backward, and if his knee was behind the pedal he would not be able to produce as much downward force because his knee would straighten too early.

A camera looking from the front would give us another important perspective. With this angle we will be able to see whether the hips, knees and feet all line up with the center of the pedal. Once again we want all the joints to align with the center of the pedal, so that all the force is generated directly through the pedal. If the cyclist's knees pointed outward rather than forward, he would be losing efficiency by generating a force that is not directly in line with the pedal. If he did this, he may also suffer from injuries as he attempts to maintain the same speed. He will need to recruit different muscles or strain ligaments and tendons to make up for his lack of efficiency

Video analysis of your cycling technique is easy to do with a couple cameras and a stationary bike. Below are 2 great examples. A side on view allows the cyclist to evaluate his position on the saddle as well as his knee and foot position.



A front on view allows the cyclist to check the forward alignment of his hips, knees and feet.



This cyclist looks to have good biomechanics and an efficient pedal stroke. For a more detailed analysis you can also use video analysis software to calculate the angles and accurately measure the positions.

Lance Armstrong will be in action again this year at the Tour De France and we look forward to seeing what he can do. Lance has spent many hours in testing wind tunnels measuring his bike performance, but we are sure he also uses this data to fine tune his biomechanics for maximum efficiency. So get out your video cameras and film yourself in action.

Why Tiger Woods has a Perfect Golf Swing

This last weekend, we once again had the pleasure of watching Tiger Woods playing in a Major Golf Tournament, the 2009 Masters. He injured his knee prior to the 2008 US Open, and the last we saw of him was winning that tournament in a lot of pain.

He may not have won this year's Masters tournament, but his swing truly is exceptional and it is always worth taking a look at some video and snapshots of his swing to do some video analysis. So why does Tiger Woods have a perfect golf swing? The answer is TIMING.

Tiger shows an almost perfect example of a concept we discussed in our last post with Andy Murray's serve. Tiger creates club head speed by perfectly sequencing and timing the movement of his knees, hips, shoulders, wrists and club. In golf, this is known as the kinematic sequence. The kinematic sequence in a golf swing is a little different to that of a tennis serve, but in the end the idea for both is to create club head speed or racquet head speed by storing and then transferring energy from hips to shoulders to club or racquet, with perfect timing.

Let's have a look at Tiger Woods' swing in slow motion. We have seen this video before, but it is a really good one. In this video we have a side-on view of Tiger's swing (side-on to the direction he will hit) and we can see the club throughout the swing. This makes it a great video to analyze. The video was also filmed with a high speed camera with a high shutter speed, which is why we can see the club so clearly in each frame, even through ball impact.



OK lets analyse this swing by looking at the way Tiger stores and transfers energy to the ball through the golf club. If you stop the video at 0:33 seconds, you will see that Tiger is now at the top of his back swing. During his back swing he turned his hips and his shoulders away from the direction in which he will be hitting in order to store up energy for his swing.

Play the video from here and we will see how his hips start to move earlier and quicker than his upper body and that his shoulders are left behind. Tiger is starting his kinematic sequence by unwinding his back swing. The timing is important and he leads with his hips in order to create more separation between his hips and shoulders and therefore create more energy to be transferred.

His shoulders then follow and at ball strike we see that Tiger's hips are now facing the target while his shoulders are almost facing directly at the camera. This perfect timing has allowed him to transfer all the energy from his back swing, first to his hips and then from his hips to his shoulders.

Here are two images of Tiger at the top of his back swing and at ball strike, created with some free video analysis software and images of Tiger's swing.

Although these are 2 different swings, we can see how Tiger creates separation between his hips and shoulders in the image on the left and how his hips are turned toward the target at ball strike in the image on the right. The shoulders have rotated quickly as they follow in sequence from the hips, in fact they have caught up with the hips as energy was transferred from hips to shoulders and the hip rotation has slowed while the shoulder rotation has sped up. The angle between the hips and shoulders at ball strike is now much less than at the start of the down swing and we can see this in the images above.

Of course the golf swing does not end with the shoulders and there are still numerous places where the timing can be off and the golfer can lose club head speed. In the video above we can look at time 00:41 seconds and we can see that Tiger's wrists are still cocked. As we play forward from this point we will see the wrists release, transferring the energy from the shoulders and arms to the wrists and on to the club and club head at ball strike.

This last sequence happens very quickly and the golfer's timing has to be perfect. Tiger Woods is the master of this timing and we look forward to seeing more video of his swing now that he is back from injury.

Send us your comments and let us know what you think of our posts. We look forward to hearing from our readers.

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