Dude it happened to me when I was 16 years old.
I tried to protect her and I basically did because they ran of when they dislocated my knee and gave me a fair few punches and kicks when I was on the floor. There was seven of them and one of me (none of my friends were there) I punched one in the face and then the other six did the rest to me.
Then 5 days later my girlfriend come to me and said I am dumping you she didn't really give me a reason why.
So basically make sure the girl your fighting for is worth it because the one I did fight for was not worth it in the end.