I had a rather indirect experience of this. I had a paper route as a kid and on one part of it lived a bully that would come out and harass me to the point where I would avoid the neighborhood (didn't go over well with people who missed their paper either). For some reason I never could bring myself to fight back, but at some point my Mom found out (I think I was asking my Dad how to fight or something and that clued her in that something must be going on). Anyway she came with me the next time and layed the smack down on that kid and I never had a problem after that.

Edit: I don't think she was actually physically violent but rather he got an earful that probably made him think there could be violence if he ever tried anything again.