As Shakespeare once wrote “For God’s sake, let us sit upon the ground and tell sad tales of the death of kings”. Mine would have to be Rocky Marciano vs Joe Louis. When I heard Rocky cried in the locker room after he beat Louis and showed no joy when he was declared the winner in the ring by the announcer says a lot of the admiration Rocky had for Louis. He said to Louis, “I’m sorry Joe”. Joe responded “What’s the use of crying? The better man won. I guess everything happens for the best.” What's yours?
Ezzard Charles' decline was very sad. One of the greatest fighters of all time, and he ended up like this. Losing 2/3 or so of his fights after Marciano. This content is protected While seeing an average fighter get permanently damaged is obviously horrible, it is especially demoralising to see one of the greatest ever like this.
Much like the OP's story, I know Larry Holmes was pained to have inflicted so much damage upon Muhammad Ali.
Duran losing against William Joppy in 3 rounds. This was a gift fight for Duran no doubt, he was never expected to win, but it's still one of saddest fights for a legend.
In his own way, Chris Eubank seems to regret the suffering he inflicted on Michael Watson. I'm not so sure about Benn's feelings towards McClellan. Eubank jnr doesn't seem to give a fig about what he did to Blackwell. Shakespeare could have written something rather eloquent and moving about those three pairs of boxers.