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Drama

I was the only guy in the defence line in a free kick when opponent placed his ball. The opponent had massive leg muscles and he was far taller than me. He scored a goal I have never seen in any football game ever, it barely touched the top of my hairs when I tried to hit the ball back with my head. The flight path of the ball was like a whirlpool: it rised just over me, it spinned to the left, it then went down and then again up so that goaltender was totally flabbergasted by the rapid change in the movements of the ball. For me, it looked like a whirlpool shot due to the whirlpool flight path.

I have tried to understand this shot now years later through golf-tennis terminology. The ball changed direction two times so it must have had:

  • topspin for changing the direction first time from up to bottom and
  • sidespin from right to left
  • second turn from left to right: how?!

now I haven't been able to repeat this shot, neither with a golf club nor tennis racket. Even physically it is hard for me comprehend it.

How can you do a whirlpool shot in football?

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I do not follow the description, is it like the diving/dipping shot that has gotten so famous lately? Something like this: youtube.com/watch?v=h1tw3t78fVE? –  posdef May 16 at 13:00
1  
This question made me think. –  Don Larynx Jun 2 at 20:53

2 Answers 2

In summary, we have this picture.

enter image description here

This picture shows the ball kicked from the right because the wind is heading towards the left. (Let's ignore for now the possibility of strong tailwinds.) Because the ball is rotating backward from the top, this ball has negative topspin - also defined as backspin.

As for the wind lines...the closer the wind lines are, the lower the fluctuations in speed (and it means that there is low turbulence//wind is heading in one direction); either way, this is unimportant and only mentioned for clarity.

For now, let's understand that a ball kicked in the above manner will have the bottom of the ball going against the wind but the top of the ball will be going in the same direction as the wind (because of the backward rotation!)

This means that the bottom of the ball is encountering air resistance.

The top of the ball will be going in the same direction of the wind. This means that the top of the ball will be facing negative air resistance. This then means that the ball, by nature, will want to move in the same direction!

As shown in the picture, there is higher air pressure at the bottom because of the two different directions of air. At the top, there is lower pressure of air. The ball will once again want to naturally move to lower pressure, just like you would want to move to lower pressure zones because it's naturally easier.

This explains why the ball, when kicked with a backspin, will stay in the air longer. For topspin, there will be lower pressure at the bottom for reasons described above - so the ball will want to move towards the bottom faster, which explains why topspin balls fall quickly:

http://www.youtube.com/watch?v=PJirUc_Dolg

In general, when kicking a ball away from you, if the left side spins toward you it will fall to the left. The worst free kicks possible would be where the ball's left corner spins towards you, because then it heads towards the center of the net, where the goalie is :P

Now that we understand that, in your situation the ball must have been kicked such that, if you were the opponent that kicked the ball, then the ball was initially kicked with the bottom left corner of the ball spinning towards you with low spin speed and switched directions completely such that the ball's upper right corner was then spinning towards you at high speed. This may be due to a strong headwind.

For extra information,

This is called the Magnus effect.

We define drag to be any force acting opposite to the motion of an object. In this case, air resistance means drag.

We go to 32:50 of the following video for a postliminary understanding:

http://www.youtube.com/watch?v=xGMnuqKexG8

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Awesome answer, this has a lot of useful information to help analyse the situation +1. Turbulence phase 35:50 and volleys 1.15:00 are pretty interesting in the last video, thank you for sharing. –  hhh Jun 4 at 23:48

More likely what happened is that the shot had little to no spin on it at all. This is difficult to perfect and hit on target, and the flight mechanics are virtually identical to a knuckleball in baseball. It probably did not actually change spin, but instead jumped about in a way that the kicker could not have even predicted.

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I have actually observed that phenomenon with different balls, thanks for pointing it out +1. The seams are enough to create the effect with no spins in the ball creating very sporadic flight paths. In tennis, I have noticed balls that change the direction after hitting the round -- not understanding how this actually works, the round somehow deflects the spin? –  hhh Jun 4 at 23:51

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