Yes, I have done this quite a few times, depending on the situation.
If 2 obvious chavs want to go at it then let them, if some chav is having a go at someone else then i'll step in.
Last time was Friday night coming back from work. Came in 2 town and there is a big house where they seem to house retarded troublesome types with no homes, all young men. Pulled up to the mini round about there to see some 6'2" skin head with his top off squaring up to some 5'8" skinny weedy nerd type. shot through town and phoned the police, did a quick circuit and ended up back at the round about. Jumped out, asked them if they new where the Kings Head was as I couldn't find it.
Totally threw them all, and kept them busy for the 2 mins until the cops turned up. Had to then give a statement.
Saw 2 guys pummelling a 3rd once while his g/f screamed so me and a mate helped him. He did most of the fighting as he's trained.
Also knocked a german tourist on his bum in front of the police in Ibiza because he smacked his g/f. He was arrested and cop just shook my hand.
Wife hates me doing in thinking it'll get me killed, but, its not who I am
I've also been stabbed/slashed twice, once was some lad trying to mug me while I was jogging at 6am in the morning, the 2nd was for stopping a guy hitting his g/f in Birmingham. Luckily neither was too serious.
When I was 14 a lad and a girl I knew were fighting, I simply asked if she was ok. Next thing, he's come back with 8 18+ year olds. They are all on drugs and luckily, I'd drank a bottle of whiskey.
I ended up barely able to see out of each eye, 3 broken ribs, 1 fractured, broken nose and brain damage. All while a copper stood 50ft away and watched. Not so tough on their own though
