Crumpling is a term used in the Street Fighter series and other fighting games to refer to a slowly falling opponent. In other games, they have their own name to this kind of animation, such as collapse.
Crumpling is signified by the character slowly falling, generally on their knees, before lying flat on their stomach on the ground. Prior to the Street Fighter IV series, opponents would only crumple when knocked out by chip damage, weak basic attacks and certain throws (in the Street Fighter III series), and could not be exploited in gameplay.
A rudimentary attempt of animating a crumpling motion can be seen in the Street Fighter Alpha series, only seen when an opponent is defeated on the ground by chip damage from a special move or super combo. (this involved the victim going through their hitting high animation leaning backwards, and then lying down on the ground afterwards)
Street Fighter IV seriesEdit
The Street Fighter IV series introduced another method of crumpling that had gameplay applications: the Focus Attack.
If a regular Focus Attack hits an opponent mid-attack, the counter hit will crumple them, leaving them open to attack. Level 2 and Level 3 Focus attacks have an inherent crumpling ability, in return for longer charge time. Focus Attack crumples are a popular way to combo into an Ultra Combo.
In addition, certain character's grabs, such as Gen's, will also crumple the foe, though they do not serve any purpose to gameplay in this case.
Street Fighter V seriesEdit
In Steet Fighter V, only certain moves can put the opponent in a crumple state, such as Karin's EX Orochi. In addition, a few characters can crumple their opponent with their Crush Counter attacks, such as Nash's Heavy Punch or M. Bison's Heavy Kick. The opponent will also crumple if a player uses a Light attack on a grounded opponent that results in a knockout.