Let me explain. Were cavemen slaying the proverbial sabre not skillful. The reference probably applies more so with slicksters. They tame their beasts in the ring with skill. Its why all these sayings are used so often in other sports and general conversation. Every now and then a bit of animal spills over into other sports as well, and we secretly enjoy it. Zidane's headbut for example. Sure it was a silly thing to do at the time but people actually enjoyed watching that. Look at the views and paradoy's which were made from that incident.
In most sports when a team or a player is getting a hammering, the commentators usually say '' If this was a Boxing match, the ref would have stopped it by now ''.
"See that guy over there with the handle bar moustache, crotch less leather chap, drinking pink champagne and singing a Shirley Bassey medley on the karaoke? He's as bent as Dave Parris!"
Like i said i get the point, just has different connotations for some that's all. Good shout, Nate Campbell literally did this when he was chasing Casamayor around a couple of years ago. He showed up at one of Casa's fights, sat ringside and threw a top hat into the ring after the fight to challenge Casamayor, didn't get the fight though.