This is going to be very subjective because I think a lot of candidates posted in here are going to be for either mental or work ethic reasons. And these are arguably just as important as chin, speed, power, stamina etc. Is Zab Judah an underachiever because he lacked mental fortitude? Is that his fault, or is it as innate as chin or power. What about Arthur Abraham, did he underachieve because he was not willing to adapt his style & increase his workrate. Or Ike Ibeabuchi, he had a lot going for him. But his favorite pastime was to ****, isn't having self control as innate & important as his reflexes, power & chin. This will just be a very hard thread to objectively contribute to. So I'm just going to list one fighter and that's Joan Guzman.
They all never fulfilled there potential. They all had the ability to achieve alot more than they did, hence why they were underachievers. Toney had a solid hall of fame career no doubt but if he been more disciplined and came to fights better shape because have been alot greater than he is
Rocky Juarez- Won the Silver medal in the olympics and then proceeded to have a career of second place finishes. David Tua and Andrew Golota- Literally the two best heavyweights in the modern era never to win a world title. Mind you fighters who have won world straps in/around their eras have been Cory Sanders, John Ruiz, Oleg Maskaev, Michael Bentt, Axel Schulz, Sam Peter, and Siarhei Liakhovich.
I want to say Naseem Hamed. I remember interviews with his trainer saying that he slacked off in training camps and never reached his full potential. As much as I hate his cockiness - he probably could've really been something in the long-run. It's a shame, in my opinion.
floyd mayweather jr. to a certain extent. has the skills and talent to be a top ATG but did not fought the fights that could have made him that. couple it with fighting once a year.