A dangerous object or being that is placed between the legs of a person unknowingly to them.
Term was originally used by Will Ferrel in Man VS Wild Will Ferrel Special.
Objects used to surprise sex a victim is NOT a crotch buster.
Person climbs down a tree, leg is over a lower branch(crotch buster). The person releases his grip expecting to land on his feet were the branch busts his crotch.