This episode makes a sympathetic character out of an old boxer, a really tough guy who took a lot of punishment in the ring, and dished it out, too. He's the victim in the beginning, the man found dead and the CSI team has to figure out who and what killed him.
The show, like many CSI stories, then delves into the dead person's life, looking for further clues and for suspects, from his old trainer to some young punks trying to pick a fight with "The Gladiator." The boxing world has a long history of fighters who took many blows to the head and wound up in destitute situations or just doing menial work. And then there are the jerks who, like the gunfighters in the old west, who still want to challenge the top dog, even if he's long past his prime. Or, you get fighters who should not be in the ring but don't want to stop the sport because they just love it. Fortunately, that's not allowed anymore but you could have "underground" bouts, which is part of this story.
All of that stuff mentioned above in this interesting episode.