A black bear can be fist fought. I carry a good knife in black bear territory. It may claw me, but I'm going for a lung puncture or a throat cut. Just big dogs with claws really. Grizzly territory, I'm carrying an Alaskan in 454. They may find my body, but they'll find his too.
Since we have examples of black bears in Oklahoma exceeding 500 pounds, I really want to see a video of some John Rambo wannabe in his Chuck Norris underwear fist fighting (or knife fighting) one.