A crossup is an attack that hits the opponent on the opposite side, forcing the opponent to change the direction they are blocking from left to right (or vice versa).
Ambiguous Crossup
Some crossups are more difficult powerful because the attacker can choose to cross up .
Crossunder
Crossup Protection
Crossup Protection is a system mechanic that allows crossup attacks to be blocked by holding either backward or forwards. Crossup Protection usually lasts for a few frames after players change sides. This serves as a slight defense against ambiguous crossups.