Any fighter afflicted with the crumpling affect will be stunned momentarily. In the air, the fighter is essentially paralyzed, but if grounded, they collapse to the floor in a weakened state. During this time, they are unable to move or act until the animation passes, in which the fighter is automatically returned to their standing position.
Unlike paralysis, the effect has a fixed duration regardless of the attack that causes it, the relative strength of the attack, or the damage of the target, and cannot be decreased by button mashing. These factors guarantee the attacker a set amount of time for a follow-up attack, though the victim's animation may shift their hitboxes in a way that makes them harder to reach.
In Super Smash Bros. 4, only Ryu and his Focus Attack at half to max charge can inflict it, but in Super Smash Bros. Ultimate, Ryu's Echo Fighter Ken was also given Focus Attack. Additionally, the newcomer Ridley can achieve it if he sweet spots his Skewer.