Forward in all directions!
Why do Goalkeepers Dive Backwards?
As a goalkeeper, I was always taught to dive forward at an angle for balls. This is also what I coach. However, many goalkeepers have a strong tendency to dive backwards. You even see this at the international level. Why is this so common when supposedly the coaches have taught them otherwise?
I encountered a fellow on rec.sport.soccer who claimed a goalkeeper should always dive backwards, since it gave them more time to react to the ball (he was obviously not a goalkeeper coach!). But there had to be some reason why the tendency was so strong. I decided to write a short program to simulate the problem and see what it could tell me.
Modeling the SituationI modeled the situation with some simplifying assumptions (see below), varying the position of the shooter and the goalkeeper, the direction of the shot, speed of the goalkeeper and the ball, and the delay of the goalkeeper's reaction time. This last turned out to be the key. If the keeper always reacts at the same instant the ball is struck, the angle of interception can never be less than square (90 degrees). However, if there is a delay - which there almost always is - the optimum angle of intercept can be backwards (greater than 90 degrees)! The longer the delay and the slower the keeper, the more "backwards" the angle can become.
I put the program into a Java applet so you can look at it graphically and play around with it. The blue spots are the shooter and the final ball position; the black circle is the goalkeeper. The lines show the path of the ball and the angle between the shooter and the goalkeeper. If the lines are green, the ball was saved and the angle of intersection is shown. If the lines are red, a goal was scored and the keeper is shown at the point they got closest to the ball and their angle at that point.
Shooter and GK Y distances are measured in feet from the goal line; X distances and the "Shoot at" spot are measured in feet from the center of the goal, with negative numbers being to the left of center and positive numbers to the right.
So, why do goalkeepers dive backwards? The answer is that sometimes that's the best angle to intercept the ball. I think instinctively, athletes will try to make the most efficient movements; in this case, get to the ball by expending the least amount of energy, at the lowest speed possible. As we can see, slower speed means a more backwards angle. And consider the case of a hard, close-in shot: by the time the keeper reacts, the ball is practically past them and their only hope is a backwards sprawl.
Why Dive Forwards?So given that the best angle to dive at is often backwards, why coach goalkeepers to dive forwards? There are still four very good reasons, three of which don't show up in this simulation. They are listed in roughly their order of importance:
To conclude, the goalkeeper response of diving backwards is to be expected, since that's where the easiest interception point may be. The human mind is pretty good at instinctively judging angles (as a friend of mine put it, "You don't have to know much about trigonometry to figure out that bus is going to hit you if you step off the curb."). Our challenge as coaches is to overcome the instinct in order to teach the players how better to keep the ball out of the net.
Some assumptions and simplifications used to create the above applet:
|© 2003 Jeff Benjamin, all rights reserved|