Guy beating up his girlfriend on the street

[BluffTHIS!]

I own firearms and so wouldn't get involved in anything without them. If he were beating a little old lady to steal her purse I would be more likely to do something. But in this case I would just call the police like you did because the usual situation is this isn't the first violent incident between them and she is one of those pathetic women who stay in abusive relationships until she gets killed or seriously injured. And because of that she could well be ungrateful and turn on you too.