You have to touch all the bases to get the HR. Ventura had a HR turned into a 2B because his teammates mobbed him at 2nd after the winning run already crossed the plate. My guess is the guy would have to crawl around, or have the opposing team carry you, like that softball player last year. In the event of an injury on a home run, a pinch runner can take the place of the hitter and finish rounding the bases. This leads to a player being able to hit a home run, but not score a run, as the pr gets credit for that. I think there's probably a similar rule where if a player is hit by a pitch and injured a pinch runner could probably touch first for him.