Roberto Carlos Dat Curve Shot gif
Adam Rifkin stashed this in Soccer
Curving the soccer ball with a kick this way is called magnus effect.
This specific type of curve is possible by hitting the ball on the valve very hard. This combination allows for the crazy swerving of the ball.
Roberto Carlos trained daily for his freekicks but he admitted that this goal was a bit of an accident, when it swerved so far to the right he expected it to be way off target.
That free-kick (Le Tournoi vs. France). Scientists say it was impossible to bend it so much with the outside of the boot? Did you think you’d totally sliced it when you first hit it? Ben Marshall, via e-mail [Shaking his head] How did I do it? I don't know. I hit the ball and, well… there are free-kicks like the ones you see Beckham hit that move and fool the goalkeeper, but mine was different because the ball went outside-in rather than the other way round. There's no explanation, no explanation… the ball was too light, one of those ones that floats all over the place like a kid's ball, and I hit it really hard – really, really well – with the outside of my foot, but I don't know… it surprised me when it went in: I thought it was going wide and when it swung so far back and went in off the post I couldn't believe it. It was an impossible goal – you'll never seen one like that again. Remember it, because it won't happen again, ha, ha. http://fourfourtwo.com/interviews/one-on-one/236/article.aspx
Since then we have seen more of these freak goals because people did this on purpose like Hulk:
As you can imagine, the player is able to put significant spin on the ball as it leaves his foot into the air. This spin causes the air on left side of the ball to be moving faster, relative to the ball's center, than the air on the right side of the ball. This difference in relative velocities causes a low pressure zone on the left side of the ball which is what pulls the ball into the goal.
This is the same principle behind baseball, and why pitchers are able to cause their pitches to move in the air. The soccer ball is much more exaggerated than a baseball though, due to the fact that a soccer ball has a much larger surface area than a baseball.
In other words, MAGIC.
Actually, this article is a great explanation: