he has some legit mental problems.
no skills at all. looks like he can throw a hard punch occasionally (just wings it), but no actual boxing/fighting skills.
also check some of the last videos on this thread, a professional heavyweight boxer tried to take his head off. Zelenoff is lucky he didn't die that night. tbh i'm surprised he's still alive.
http://www.adarq.org/boxing/charlie-zelenoff-greatest-hits/15/