If he sneaks up on the chimp and knocks it unconscious with a baseball bat, I guess there's a possibility. In any close-quarters active combat situation though, the human would get one or two swings out and the chimp would mangle the human.

Then you stand over her/him (chimp) and finish it off. With blood in your face, your a big disgrace.....

Chimp. Weather or not the human is armed.

They go after the face, hands, and groin. Very hard for anyone to effectively fight back if they're hand or face is being mauled at the time. And the groin... well, I doubt even Bruce Lee has the willpower to stay on his feet if it's literally ripped off of him.

Most martial arts would be... ineffective at best. Martial artists are trained to fight other PEOPLE, not wild animals. A chimp is smaller, moves more unpredictably, and is far stronger, faster and far more savage than most humans. Blunt weapons probably won't work against an enraged chimp unless you get in a few good blows to the head and face, and a knife gives you a better chance, since the chimp risks bleeding out (plus more likely to actually hit something vital, like an artery or major organ.)

But once the chimp manages to get within their reach and nobody else is around to help... you're doomed.

It's hard to swing a baseball bat, or anything else, after the chimp rips your testicles off with its bare hands.

you know the saying monkey see, monkey do, right? It's why you never throw anything at them when they're all sitting in a tree or whatever, because they'll all start throwing stuff back.

grab a baseball bat and the chimp is gonna want one too.. and probably take yours..