[kokoloko]

Notice how the ball in Pirlo's free kick is barely spinning, goes very fast and the path is very unpredictable. It's called a "Folha seca" and it exploits the turbulences to make the ball drop at the last moment. Very spectacular, but hard to score consistently.

[eyko]

It's spinning, and the amount of curve matches the amount of speed. The unpredictability comes from the fact that the axis is also spinning, but very slowly. It's hard to get the topspin and rotation on the ball, and still hit the target. But these guys train shots for a living.

[dmoo]

If you have a few minutes have a look at Juninho, one of the best ever. https://www.youtube.com/watch?v=NesfdRNtwsE

Also don't forget the boots are designed to work the ball, for example http://en.wikipedia.org/wiki/Adidas_Predator

[adestefan]

This is the same principle that makes a knuckleball drop unpredictably and very, very difficult to control. The way that a great pitcher can control a baseball is amazing to watch.

https://www.youtube.com/watch?v=iiSucVCuc8g