EVENT_DISPLAYKNEE is a Game Event.
This event is run whenever a shrunk enemy is being crushed, i.e. when knee_incs is greater than 0. Set RETURN to -1 or 1 to disable the foot animation.
This does not affect the slot 1 kick, or the quick kick.
Interestingly, it appears that originally this animation disabled the weapon display, like EVENT_DISPLAYACCESS, but it currently instead lowers the weapon. As such, there is no difference between setting RETURN to 1 or -1.