EVeryones acting like Bara is some professional wrestling match, no he's in a fist-fight, in an enclosed area where you don't just grab the other guy and magically get him into a chokehold and win the fight.. Granted, most of the ideas would work if it was a wrestling match with rules and stuff, but its not.
ALthough some people have given some good ideas, but the best would be to charge back at him as soon as he stands up, that way you can catch him off balance, and he might be surprised. If you find yourself in a position where you can't run back however, I would suggest blocking/deflecting his first punch then hitting him twice in the stomach or face. Also try yelling a lot, depending on his personality it can work.