Just a few years ago I found myself as the center of a 5 on 1 circle of violence after a few guys figured they'd have some fun with one of my friends. He took off and left me to fend for myself. And I'd do it again without hesitation.
But this guy from the train was a special case. There's a certain level of violence that people just aren't accustomed to seeing up close in real life and you can't realistically expect anyone to process all of that and make a split second decision.
Besides, everyone knows about
retard strength.