The reversal is a counter-attack when the user block the opponent's attack, then unleashed his or her attack which causes a shockwave to the opponent.
In vs. the World
In the film, Scott uses the attack, which is very much the same as in the graphic novel. So it no longer need to go to detail.
In the Game
Each playable characters in the game have a counter-attack that act like the Reversal, just with diffrent amount of style.
This is a reference to one of the fighting games' techniques, the reversal. The reversal is almost the same thing with Scott's Reversal, so it no need to go into further detail.