In these situations doing too much can sometimes get you into deeper shit. A friend was threatened with a knife while walking home from a club, he beat up the mugger, but because the security footage skipped in 6 second intervals they didn't have enough to say it was self defence. The charge was raised to causing "permanent disfigurement" and he is facing the fact that he may have to kiss his law career goodbye. Most peaceful person you could ever meet, sadly he was a giant too, so arguing defencelessness is not really an option. I wonder if someone had stepped in, would one of the scum try to sue? In the states it seems too easy.