Alarming Bus Trips

I'm on the bus with Asha taking her to a birthday party when I hear a squeal from the back of the bus. It peaks my attention but I don't think anything of it. A few minutes later it happens again and I can see that close the the back of the bus a man and a woman are sitting beside one another and the woman looks upset. As the bus moves along it's becoming more and more clear that the man is somehow hurting the woman (I can't quite tell how). I'm becoming concerned about letting this go so I tell the driver that I think there seems to be something up with the couple at the back. The driver says OK thanks but keeps going. Finally, she yelps again and I tell Asha to stay where she is and I go to the back of the bus. Something has heated up between the guy hurting the woman (I'll call him jerk from now on), and another guy sitting opposite them (I'll call him Ted-although I don't know him or his name). Ted saying things to jerk that he'd like to take jerk outside and beat the crap out of him. Jerk's responding things like "fine--anytime". It seems clear to me that Ted is on a similar page to me and sees jerk abusing his girlfriend or partner. I ask Ted if he needs any help but he doesn't quite understand me. I turn to jerk's partner and ask her if she's alright. She says "I'm OK". I turn to Ted who says "she's not OK". I think Ted's right. Ted and jerk continue by trading insults and challenges whereupon it seems like it's Ted's stop and, all the while Ted gets off the bus. The driver has come over by this point and suggests to the woman that she sit closer to the front. She moves to a two-seater in roughly the middle of the bus and I go back to be with Asha. A few seconds later jerk moves beside her. I go over and politely ask jerk to move. He says he says he just wants to talk to her. I repeat the request and he insists he just wants to talk to her. It's clear he isn't going to move. I shrug my shoulders and go back to my daughter. By this time it's out stop so I make sure the driver knows that the jerk is beside her again and get off.

I feel really badly about this. I wish I had done more. Maybe I should have been more forceful with the jerk. Maybe I should have insisted the driver call the police. It made me question some things. I guess there will be people in the world who will continue to do bad things no matter how nicely you ask them not to. That sounds ridiculously naive but it really was a shock to me. Particularly as a social worker and someone who really believes there are peaceful alternatives to every conflict. Am I wrong?