Presumably turns the target’s knees spongy, making it difficult for him or her to walk.
References from the canon
- During the a riot that took place during the Puddlemere/ Holyhead game, a group of Puddlemere supporters were using this curse "in retaliation" to the Jelly-Brain Jinx, according to one Puddlemere supporter (DP).
Magic Type Curses
Incantation none given