Very good points, Henry, thank you. This is more prevalent than one might think, that is, finding yourself in a place where there is violence going on.
The police even, will tell you to just be a good witness, instead of trying to be a hero.
Now, I think that if the attack continued upon the poor girl, I would yell out to other able bodied persons, including myself, to tackle the guy to stop him and not to hit him. This does work in most cases, where there are cameras, and also avoid revenge/retribution.
The most worrisome thing, and I have investigated similar cases, is if you do something that places other people at risk...you will never live it down...if someone is killed or injured because of your actions, in addition to your being sued for negligence.
One extreme case I handled down the South Shore, involved a nice restaurant with a bar on the main drag, and where on a Sunday afternoon the tables were occupied by families having dinner.
A bunch of 'bad ass' bikers roared in asking to be served drinks. The bartender complied but at one point the bikers became raucous, upsetting the patrons.
The bartender shut them off.
So they said 'We'll be back in numbers' and tear this place apart.
1. The patrons continued eating instead of getting the hell out of there.
2. The bartender failed to call the police and ask for a couple of officers to stop by as a deterrent.
Sure enough, 15 minutes later the bikers came back with baseball bats, not only destroyed the bar but hit a poor guy over the head, who was eating dinner with his family, killing him.
The estate filed a wrongful death action against the bartender personally and the owners of the restaurant.
Stupid people all the way around.
And as I have written before, many times a martial artist who thinks he is really tough...will have a tendency to stand his ground, instead of practicing avoidance, with the result he'll end up in a hole in the ground, while his sempais fold the Sanchin arm position back into a 'Sanchin salute'
The world is an ugly place.