Predicting the Direction of a Penalty Kick

The 2010 FIFA World Cup is producing some exciting football. As we move through the knock out rounds and a winner must be decided for each game, the possibility of penalties for a game that ends in a draw becomes very likely.

ESPN's Sports Science program recently did a comparison between baseball hitting and the possibility of a goalkeeper saving a penalty kick. The presenter, John Brenkus, concludes that it is more difficult for a goalkeeper to make a save than for a batter to get a hit. The overall batting average for 2009 was .258 or 25.8%, while the annual save rate for penalty kicks is around 22%. Watch the Sports Science clip here.



Although it does seem almost impossible to make a penalty save, goalkeepers may be doing as well as they are because they are reading the kickers body language before deciding which way to dive.

A recent study by Gabriel J. Diaz of Rensselaer Polytechnic Institute, used motion capture technology in an attempt to determine clear indicators for the goalkeeper, that would help them to guess the direction the ball will be kicked from the penalty spot. This may suggest why goalkeepers guess the correct direction about 57% of the time (as suggested in the Sports Science clip), rather than only 50% of the time.

In his study, Diaz identified five reliable indicators of the direction the ball will be kicked. He discovered that four of five of these indicators were used by people (not goalkeepers) he tested that were able to identify the direction the ball would go before it was kicked. Read more here.

Two of these indicators are the angle of the hips as the kicking foot swings through and the angle of the support foot on the ground prior to kicking. These two indicators are known to football coaches and may already be used by goalkeepers.The other three indicators are "distributed movements", co-ordinated movements that balance the body, and have not been discussed by coaches or soccer players previously.

The idea that motion capture and or video analysis can be used to improve performance is not new to any of us here. Diaz rightly suggests that these predictors, including the distributed movements, could be pointed out to a goalkeeper and possibly give them an advantage. They would still need to be able to process these indicators and make a quick enough decision to gain an advantage and that may not be so easy.

Some great 2010 World Cup quarterfinal match ups are coming together. Argentina v. Germany and Brazil v. Netherlands should be some high tension and hopefully highly skilled encounters. We hope there are no penalty shootouts. But if there are, try and pick out the direction the kicker will go by watching his hips and standing leg and any other movements you think give it away. If you are a goalkeeper, let us know how you guess direction of the penalty kick.

How Polyurethane Swimsuits Affect Swimming Mechanics

The World Swimming Organization FINA has recently made rules which will ban the new polyurethane swimsuits in spring next year. The FINA World Championships are taking place this month in Rome. Records are being broken, wins are being challenged and the polyurethane suit as at the center of all this controversy.

At the 2008 Olympic Games, Speedo introduced the LZR Racer swim suit that included some polyurethane panels over areas of the body at which the highest drag is experienced. The idea was to squeeze any loose body tissue (muscle or fat) that could cause water resistance. This would reduce drag and therefore increase the swimmers' speed in the water. Recently swimsuit manufacturers decided that instead of just making panels of polyurethane they would create the complete suit from polyurethane.

A full body polyurethane suit allows an air pocket to be created between the water and the skin. The resistance of air is much lower than that of water and therefore the drag in the water is reduced. The suit also aids in increasing buoyancy. Buoyancy is a measure of how well the swimmer floats in the water. A swimmer (without a polyurethane suit) will generally use more of his kicking power to stay on top of the water. The advantage of the higher buoyancy is that he can now use that kicking power to propel himself forward.

This decrease in drag and increase in buoyancy brings up two important questions: does the polyurethane suit change the biomechanics of the swimmer and will the swimmers need to change their kicking motion or even their stroke, when they are forced to abandon their speed suits next spring? Video analysis can definitely play a part in identifying how the biomechanics may change.

At the FINA World Championships, Michael Phelps finished second to Paul Biedermann of Germany. Phelps was swimming in his Speedo LZR swimsuit with polyurethane panels, while Biedermann was wearing a full body polyurethane suit. Biedermann also smashed Phelps' world record in the same race. Did the full polyurethane suit provide an advantage?
Take a look at the video here:



Unfortunately this is TV broadcast video and often the angles are not great for analyzing video. However as you watch, notice how Biedermann remains high up in the water particularly at the end of the race compared to Phelps. In the final 25 meters of the race we can see how Biedermann's legs remain above the water and kicking hard. His kick at the top of the water is propelling him forward quickly. Phelps' legs are deeper in the water and he therefore is using much of his kicking power to stay above the water rather than to propel him forward.

Before we jump to any conclusions that the polyurethane suit gave Biedermann the advantage, we need to remember that there are numerous other factors. Fatigue would definitely be a factor. If Phelps was fatigued at the end of the race and Biedermann was still strong, this would explain how Biedermann continued kicking at the top of the water. Of course the buoyancy of the polyurethane suit may have allowed him to conserve energy throughout the race. We also do not know what normal kicking (without a suit) is like for both swimmers.

To truly understand whether the ban on the polyurethane suit will make a difference to the swimmers' biomechanics we will need to analyze the swimmers independently, comparing their swimming motion in the suit and how they swim without the suit.

We will continue to watch the FINA World Swimming Championships with interest and will also look forward to seeing how the ban on the polyurethane suit will affect the swimmers technique in the future.

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Video Analysis of a Soccer Penalty Kick

This weekend was full of sporting action, Boston Marathon, NBA playoffs and much more. We also enjoyed watching some major upsets in the FA cup soccer semifinal games played at Wembley stadium in England. For those of you not aware the FA cup is the premier soccer cup competition in England and is watched throughout most of the world.
In this years semifinals, we saw Chelsea defeat Arsenal on an unforgivable goalkeeping error, but in The Video Analysis of Sports this week we want to look at the other game where Everton upset the favorites Manchester United on penalty kicks.

Penalty kicks sound easy. The striker takes a shot at the goal with only the goalkeeper to save it and all the measurements are in the strikers favor. The international goal is 24 feet wide by 8 feet high, the penalty spot is 36 feet from the goal and the goalkeeper cannot move forward off his line before the penalty kick is taken. This means that he cannot close the angle.

Penalty kicks however are not as simple as they sound, especially at the end of a game in order to break a tie. There is a lot of pressure on the striker, he or she is expected to score the penalty and if he misses his team may be eliminated from the competition. In international and pro level soccer we see strikers often trying to fool the goalkeeper into diving in one direction and then try to shoot to the other side of the goal. When they score this way we all admire their skill and deception, but if you want to make sure of scoring then there are some specific techniques to use and we will discuss them here.

Below is some video of the penalty shootout between Manchester United and Everton on April 19, 2009. You can see evidence of much of what we will discuss today.


Berbatov (the 2nd penalty taker) and Ferdinand (the 4th penalty taker) both of Manchester United try to deceive the goalkeeper but do not use good technique to shoot and see their penalties saved.

We see some examples of good penalty kicks in this game too. Vaughan of Everton takes the best penalty of this particular shootout as you will see in the video. So what makes this a good penalty. Vaughan does everything right here. He wants to place the ball in the top corner of the goal net with as much power as possible. By aiming for the top corner with power he reduces the chances of the goalkeeper making a save even if he does pick to dive in the correct direction (which he does in this case).

What about technique? Well Vaughan does that correctly too. Here are some of the points to look out for as you watch the video above. Pause the video if you can and look closer at some of these points.

1. He picks the direction he is going to kick the ball and does not change his mind. Changing his mind might cause a miss kick and as he is going for the top right corner with power he is not concerned about the goalkeepers decision.
2. He runs up and plants his support leg (left leg) on the side of the ball with the toes of his left foot pointing in the direction he is going to shoot. This gives him the support base he needs so that..
3. He keeps his head down looking at the ball as he strikes it. This will keep the ball from flying to high. If he lifts his head, he is likely to get his foot under the ball and may lift it over the top of the goals.
4. He kicks the ball with the inside toe part of his boot (see time 4:28 in the video). He does this in order to create spin on the ball. He actually aims at the goal post but uses the spin to turn the ball back into the goal net. If he kicks the ball with his laces he may be able to create more power, but he will not be able to create spin and therefore he would need to aim more directly into the goal, giving the goalkeeper a chance to save or running the risk of missing wide.
5. He follows through with his kicking leg, bringing it up to waist height while keeping his head down. This allows him to produce the power he needs to ensure the goalkeeper has no chance of saving this penalty.

So thank James Vaughan of Everton for that real situation clinic in taking a penalty kick in soccer. We are looking forward to a fantastic FA cup Final on May 30, 2009 between Chelsea and Everton. Hopefully there will be no penalty kicks to decide the champions, but if there are you know what to look for.

Let us know what you think of this particular penalty shootout or if you have any tips or tricks of your own for penalty taking. Comment on this blog or send an email to dudley@sadakallc.com or dennis@sadakallc.com .