My man Kenny Norton was a natural born athlete. He was superb at college in field competitions and was also a prospect for the NFL.
Foreman could make a great wrestler. Carnera was a great wrestler (one of the multi-sport champions boxing can take pride in, like Vítali.)
I reckon Sonny Bill Williams could have turned his hand to Rugby, whilst Leon McKenzie would have made a decent football (soccer) player.
Most of 'em. Coaches/managers will tend to find a use for an individual with inhuman balance, speed, (learned) relative ambidexterity, strength, flexibility, competitive spirit, stamina etc.
Yep, he's the easy one. He could have had a pro football career, or a pro track and field career. Dude was a one-man track team in high school.
Had he taken up football instead of boxing, I think Ali would have been one hell of a linebacker or tight end. The thing that would hold a lot of boxers back in a lot of sport are (a) size … not a lot of use for a 125-pounder in most pro sports; and (b) foot speed (as in sprinting type speed), which is useful in nearly any athletic endeavor. I vaguely remember Marvin Hagler on the ABC “Superstars” program where athletes from different sports would compete in various athletic endeavors and iirc he came in dead last in the 100-yard dash. Joe Frazier, of course, nearly drowned in th swim competition.
Roy Jones Jr. for one. Vaguely recall him participating in a semi pro basketball game right after a pro fight. That's one heck of display of athleticism.
Paul Berlenbach, the Astoria Assassin was World light heavyweight champion, and also prior to his pro boxing career, was the 1922 and 1923 AAU National Wrestling Champion
It was kind of a developmental league, pro but the equivalent of Double-A or Triple-A baseball (before G-League came along for NBA) and he played BEFORE a title fight on the same day iirc … I think it was the Eric Lucas fight? Roy had to literally invent ways to challenge himself.