Darryl Jenifer, 55, the founding bassist of the Bad Brains, has known the two since they were boys. “They’re both like my little brothers,” he said. “I don’t get up in between that. When the wounds are deep, they’re beyond repair.” Mr. Jenifer described Mr. Flanagan as the “Dennis the Menace” of hard-core, but added that he had seen a real change in him. “When you get older, you have to act accordingly,” he said.

For Mr. Flanagan, aging also means leaving things behind. “Scenes are for little kids,” he said. “If you’re grown up and still holding onto a scene for identity, then you haven’t grown up. You’ve just gotten older.” This could be interpreted as a jab at Mr. McGowan, who is a kind of elder statesman of the scene, giving hard-core-themed walking tours of the Lower East Side and having written two books, a memoir and a vegan cookbook with an unprintable name.

The Cro-Mags have not featured Mr. Flanagan since 2002. This is something that he, as a founding member, feels ill about. “I’d be happy to play a show with all of them,” he said. “The ax should be buried, especially at our age.” Since the stabbing, that does not seem likely.

At the Renzo Gracie Academy in June, nine pre-teenage boys and girls stood at attention before Professor Harley, as he is known to his charges. Mr. Flanagan, who is a father of two boys of his own (Harley, 13, and Jonah, 11), was very much in his element, smiling as he guided the students through calisthenic warm-ups and the basics of grappling and holds.