I once attended a Mike Tyson fight. If you think his fights are vicious on television, you shouldn't see them in person. Tyson hit the other guy so hard that we could feel it in the bleachers.
Mike Tyson may be the stuff nightmares are made of, but I know of an entire league of guys who are even more frightening. In Japan, this league is called Pride Fighting; in America, it's known as the Ultimate Fighting Championship. In both places, these guys are just plain devastating.
These are mixed martial arts tournaments. This means that the nastiest guys from every imaginable discipline come and knock each others' blocks off in a few-holds-barred competition.