Biru is correct. Oyama Sensei did in fact fight bulls barehanded and killed several of them. To be clear he used Karate, but the actual killing was done by wearing the bulls down the breaking their necks by twisting them. During his life Oyama fought 52 bulls. He broke the horns off of 48 of them (horns up to 4" in diameter), and killed 3. so is it possible for a Man to kill a bull, yes, is it likely that the average person could do it using only his body, doubtful.

Used to happen all the time in foreign countries where they have bull fighting. Most of the time the bulls lost......but now and then didn't. I understand that a lot of them no longer kill the bull at the end of the spectacle.

Hand to hoof? No weapons allowed? Then possible but highly unlikely

Oyama san did such on two or three different occasions and it was filmed at least once.