tap the d pad forwards just as the ball is about to hit you, its the new feature that came out in SF 3, you can tap forwards or down just as an attack is about to hit you....if you do it right it interrupts the opponents attack and gives you a brief chance to counter without them blocking, also stops you taking damage from special moves plus you can parry in the air....its tough to get down properly but cool when you do, allows some sly tricks especially in vs mode.