Snapback is the ability to force an opponent's character and switch it with the one in reserve. Only four characters are known to have Snapback and those characters are:
Alex - Take your arcade stick/controller pad and charge back, then tap forward+C, hitting the enemy with his elbow -> delay, wait until the elbow flash animation is done -> then do DP+C (Forward -> Down -> Down+Forward Heavy) doing a drop kick animation and kicking out the enemy.
PTX-40A - Take your arcade stick/controller pad and charge back, then tap forward+C, hitting the enemy with a charging elbow, pushing them off screen.
Hakushon Daimao - Take your arcade stick/controller pad and motion HCB+C, his bottle sucks your enemy up, then spits them out of the screen.
Gold Lightan - Take your arcade stick/controller pad and motion HBC+C doing an air dive kick right into your enemy (Note: This has to be done when your enemy is jumping, otherwise, your leg will hit the ground, and you will not get Snapback to work).