Eventually, the woman sat down, still yelling epithets at the man, and we went a couple of stops like that. At Coolidge Corner, she got out, still yelling at the man, who was staying on the train. She stood at the doorway as others got out, yelling curses. The man was mostly ignoring her. She was in the way of people getting on the train at this point, and a visually impaired white woman (carrying and using a cane to navigate) said, "Excuse me," at which point, the irate woman turned her ire on this hapless individual. I'd like to say that she immediately realized that she was dealing with someone in an unusual degree of psychological distress and let it go, but she didn't, and it soon escalated to a full on shouting match, which, moments later, came to blows.
By this point, a large crowd had gathered, and stook around watching as these women shoved and hit each other. I was appalled, and without really thinking about it, I put myself in the middle of their fight, pushing them apart. They kept striking at each other, and I have to say, I don't think that's the intended use for your standard navigational cane, but I think I avoided any major blows. Eventually, someone else in the crowd stepped in and pulled the seeing woman away. They continued to yell at each other and to attempt to resume their fight. I thought people only acted that badly on TV. The black woman broke loose at one point, and hit the blind woman, who fell and hit her head on the sidewalk. After that, enough people were stepping in that she was being kept away from the woman who was on the ground.
Shortly afterwards, the police arrived, and based on people's stories, focussed immediately on the black woman. While she was obviously the prime antagonist, people certainly rose to her bait, and I don't know who threw the first punch. She defended herself to the police officer by hiking her dress up to her waist and showing the officer where the other woman had hit her (around the ribs). I decided I didn't have any useful information for the police, and went on my way.
Mack thinks it was dumb and dangerous to get involved, and in hindsight, I suppose that's true, but I really think it was the right thing to do, anyway. And I'm okay, so it worked out. I feel like I've done my work in the world for the day, though, and I want to go home and nap.