If Prust had fought Phaneuf, that would be a heck of a solid tradeoff in any game situation, but it was pretty clear that Phaneuf wasn't going to fight.
This is the 3rd or 4th game this season that Prust has run around a little bit, the second game he's done it against Toronto. Prust leads the entire NHL in penalty minutes for a reason.
He got away with it in this instance, but usually when you drop your gloves and the other guy doesn't, you get a penalty. I'm not suggesting that Prust be a healthy scratch, the Canadiens can't afford to do something like that with Rene Bourque sidelined, and he's actually playing pretty well with Gionta and Plekanec, but perhaps it's time for Therrien to sit him down and tell him to pick his battles.
Prust is a heart and soul kind of guy, and his teammates clearly love him, but could he be better served by chilling out?