(A condensed version of this story first appeared in Friday’s USA TODAY .) When it comes to the unwritten rules of the training that mixed martial arts fighters put each other through behind closed doors, UFC lightweight and MMA veteran  Yves Edwards has a simple way of looking at it. “The gym is like Vegas,” Edwards told MMAjunkie. “What happens in there should stay in there.” Call it an unofficial code that MMA fighters expect one another to abide by.