Awhile back, in an official-looking USFS pamphlet, I read that black bears will always retreat-- even with cubs-- if the human charges the adult bear with waving arms and unrestrained screaming and yelling. I've always kept this technique in the back of my mind should the need arise, and have actually used it to help repel an aggressive, charging javelina. In the case of the javelina, the primordial screaming and arm waving wasn't enough and I had to resort to throwing rocks and running for my life until it was satisfied that it had made its point.
I would hope that your typical black bear, shown a similar defensive/offensive technique, would not have as much to prove.
