As for me I think not fighting back is a mistake.... Although it depends on a situation... Sometimes you just don't want to get hurt even more...
I had problems like that in school in the beginning, it was getting really bad... but you know what cornered frightened creature does? Attacks! And one day I realised that they only bully you if you are scared...
Since then I didn't have problems with bullies... On contrary, I was sticking up for others! Didn't make me a very popular girl with the "cool ones", but then it's understandable, because they got some bruises from me... Got me in trouble a few times that...
I'm not that wild anymore, hehe, all grown up... avoid confrontation...
But seeing someone being bullied makes me really mad, I mean proper mad... especially if it's someone I love.... It's like I still have that switch somewhere that makes me tremble with anger sometimes...