The way I see it, it it's worth fighting for, it's worth fighting dirty for. There is no shame in that. Especially if you are outnumbered.
Just remember though, if you kick him in the balls, and he gets back up...you better be prepared to knock him the fuck out, or run, cause he is going to be pissed. Really pissed.
Also, never underestimate the value of a good eye gouge. If he can't see, he can't hit you, right?
Good luck.