There is no question. An MMA fighter would rock the shit out of any boxer. They have to deal with a great deal more than a boxer does. A boxing stance is so open for a take down, it's not even funny. They'd get taken down, and tapped out.

The first UFC's were no holds barred. Pulling hair, head-butts, eye gouging, you name it, it was allowed. It wasn't until they were banned when they got some sense. UFC 1, Joyce Gracie single handedly killed every fighter, without ecen throwing a punch. Most of the fighters in the tournament specialized in boxing. The only time boxers will prevail over MMA fighters in a combat sport is in boxing, and maybe kick boxing.

With that being said, if Pretty Boy Floyd had two or three years of Brazilian Jiu Jitsu, he would breeze through MMA with no problems at all.