Not in that sense, but there has been a fight for my honour once. I was at a gig, and there was a really sleazy guy behind me who was being really inappropriate - I didn't know him, and he was being very forward and touchy-feely. When he wouldn't leave me alone, despite me trying to move away and telling him to stop, another guy I didn't know got into a fight with him about it. It didn't get serious, but the sleazy guy scurried off quite quickly. It was good to know that a stranger was looking out for me, not wanting me to get into trouble.
But in terms of fighting for a potential girlfriend/boyfriend, I think it's pointless. I'm very much of the opinion that relationships don't work if forced. If something is going to happen, it will happen naturally.