You jump in and do whatever is necessary to protect him! Period. And no, it doesn't matter wether or not your brother started it. And to say you wouldn't have done the exact same thing is either hypocritical or ridiculous.

And to those who will cry turn the other cheek: no way, not in that situation. It's 5 on 1, you're defending him.

And no, that doesn't mean I think everything we did in the brawl was justified.