"Raph, have you lost your mind?!"
"Easy there, cowboy, they're down!"
I really like the call-back here, putting Raph in Leo's position, stopping someone from doing something terrible in a blind rage. These moments are just minutes apart from each other, in the same episode (Meet Casey Jones).
Some people might say that it's too quick a change from Raph here, that he'd sooner join Casey's brutal vigilantism than intervene, but I'd disagree for three reasons:
Raph neither wants nor likes to be the guy that flies off the handle. Minutes ago he almost hurt his brother, badly. He'd wanted to hurt him bad, and when he came to his senses he was horrified. When he was alone he screamed 'What's wrong with me?'. He is aware he can't control his emotions and he doesn't know what to do about it, and he's scared.
Raph has a moral compass. He intervenes with Casey as Leo did, because he knows that's the right thing to do. Raph just got a very real and scary wake-up call to the consequences of unchecked rage, and this makes Raph especially sensitive to it. Of course, awareness doesn't mean change - Raph does lose it again in the episode, which is realistic - but it's a step towards change. Stopping Casey from making the same mistakes is part of that.
Raph has had a chance to calm down and think. When he's calm, he can think and reflect, and that reflection has given him determination to be better. Everything Raph tells Casey has come from that, and it's all the things that apply to himself.
