Tonight Terence Crawford defeated Amir Khan. The bout ended after Khan could not continue following a low blow. The shot was ruled accidental and Crawford was declared the winner via TKO.
So can you win a bout after hitting an opponent with a low blow? The answer, in some jurisdictions, is yes. New York, where this bout occurred, is one such jurisdiction. New York has regulation on the books that a fighter must wear a ‘foul proof’ groin protector. The idea is that groin protectors exist that are so flawless that no fighter can actually be stopped via low blow. I doubt there is much scientific literature backing this idea. In any event New York has the following applicable regulations fighters should be aware of before competing in the Empire State:
Combat Sports Law 