depends on the fighter, i still remember when i was a young boxing fan, not understanding how matthew saad muhammad couldn't beat anyone after he lost the title. Made no sense to me at all, if you can't beat a championship level fighter, you should still be able to beat a lot of other fighters. But it's really a mental sport. I'm sure the physical attrition is a huge factor but I would believe that there are many cases of fighters who are just broken by a tough fight/loss. Here's a few to conjecture.
Frazier--Ali 1- neither man was the same again, Ali fared a little better, probably because he wasn't typically a full throttle, face first fighter, but neither were ever able to match their outputs and their intensities of the first fight.
Ali-Frazier3- Both men were thought to be on the downside and no one expected a classic, especially with ali winning the rematch and beating george foreman, Frazier was thought to be finished. What wasn't finished of frazier before was taken here, Ali was never the same either and would only go on to mostly boring fights and only scoring a couple more knockdowns in the remainder of his career.
Camacho-Rosario: I don't really know if this fight ruined camacho, I really don't but it's a popular theory and there is evidence, even with camachos own words after the fight. A lot of fighters just plain lose interest in the sport, Camacho seemed to be one to me.
Honeyghan-Curry: Curry was thought to be the number one pfp by some people at the time, that's right, even better than hagler. Curry had beaten a string of strong competitors, Starling, Milton McCrory, Colin Jones, good fighters. Honeyghan came in looking stronger, bigger, faster, more determined and not a bit intimidated by the reputation of curry, Curry quit in his corner and was never the same again.
Fighters who have killed fighters also have a mixed history of success. Sugar Ray Robinson, Nigel Benn, Chris Eubank, Ray Mancini, one of the Ruelas bros., I think there are stories of fightes actually seeing dead opponents in the ring during a fight, max baer i think said he saw the ghost of a dead opponent. Ruelas said it too but he didn't mean it literally.
Chavez-Taylor: I still remember reading how many people heard Taylor slurring at the post fight press conference, Taylor was a case where he always had heart and courage so I don't think he was that diminished by the beating so much as he just fought stupid a lot of the time and seemed to have a masochistic streak. The shopworn Taylor in the rematch at least showed that he had no loss of courage and fire.
Clay-Liston: Foreman could also be mentioned but he did manage to stage one of the miraculous comebacks in boxing history, Liston never did. He was broken after the two Ali fights, still good enough to beat some fighters but the beating he took from Leotis Martin was frightening from what I remember, Leotis never fought again after that win because Liston injured, i think it was his eye. Liston, prodigious abilities that he had, was still able to half kill Chuck Wepner a few years later.
Marlon Starling-Mark Breland: Mark Breland was one of the all time greats as an ammie and he was a successful pro but Starling was a spoiler, Breland fought well in the rematch but still lost and then was handed another title shot, forget against who, but it sounded like one of those setup title shots, then, he fought Aaron Davis and got kayoed again and like Curry, finished his career getting kayoed by clubfighters.
