A groin attack is an attempt to cause pain to the groin area of one's opponent. The technique can be quickly debilitating, due to the large number of sensitive nerve endings in the testicles of males. This technique is considered to be the specialty of Tum Tum who practices it incessantly on his grandfather's training dummy.
All three of the boys seem to already know the power of this strike having a strong reaction when grandpa points to this area. Rocky even used this technique against Tum Tum when a slap on the slide of his head failed to stop him from making kissing sounds while he spoke Emily on his tin-can phone.