Good Samaritan gets jumped for standing up to stalkers at Guy-Concordia

Saturday night at around 11:45 at Guy-Concordia metro station, a young man started shouting :

"Hey, just so everybody knows, these two guys are following and harassing these girls right here, you guys are all witnesses! They don't want nothing to do with you, leave them alone."

The two guys looked in their early twenties, and the two girls they were allegedly following looked a bit younger, somewhere in between 17-19 yo.

Our two harassers then got pretty angry and started threatening the guy who called them out. That's when a security guard (not a metro station employee, just a Garda who probably had just finished work) stepped in and tried separating them. A group of girls on the other side of the tracks started insulting and boo'ing the two men. The good Samaritan then slapped the cap off of one of the harasser's head, and the metro arrived on the other side of the platform (the side I was on). The two stalkers started going at it with the other one who called them out. The security guard was able to get the second dude off by pulling him by the hair, dragging him away and talking him out of it, while his friend kept fighting one on one with the good Samaritan.

Unfortunately, his opponent was able to get a few punches in, but mister good guy managed to rip a part of his jacket and throw one of his shoes into the tracks. The two girls stood there on the platform, as well as two other men, and they just watched everything unfold. I got on the train and went on with my night. I don't know the rest of the story.

I've had many crazy violent encounters in the metro, but this is probably the first time I witnessed a fight break out like that.

What do you think is the correct approach when you witness harassment in public?

Do you think the guy who stood up for the two girls did the right thing? What would you have done?