Concussions

Yeah, but UFC is strictly monitored by the athletic commissions, and doctors are constantly examining the fighters before and after the fights. However, it's definitely an unavoidable part of the sport — look at how fast Chuck Liddell progressed from killing machine to "glass jaw" after repeated blows to the head. Not only that, but forcing fighters to wear gloves actually makes the problem worse because they can inflict more blows without breaking their hand. I dunno, it might just be like boxing where it's accepted because it's been around for so long now.