Re: for good athletes transitioning to boxing, is the chin the biggest factor?
Was it Mitchell's chin? He didn't get knocked out cold, he just took a lot of solid punches. Punches that he didn't have the experience to ride out or to get away from. Mitchell might have a weak chin, but taking solid, direct shots will affect anybody. He didn't just take one shot and collapse, he got hit with a lot of punches.
It's going to be difficult to transition from a sport where athletes plays "tense" for 2-4 second bursts, to a sport where the athlete needs to be "relaxed" while punching and avoiding being punched for 3 minutes at a time. There isn't much carry over from football to boxing other than both sports have contact.