The coach wasn't pleased about the forward's first of the Stanley Cup Playoffs, which came in Game 2 against the Columbus Blue Jackets on Saturday, a cross-checking infraction at the end of the first period.
Cassidy had more of a stern tone Wednesday, the day after Marchand took his second penalty of the series in Game 3, for high-sticking in the second period; in each case the Blue Jackets scored on the ensuing power play and won the game. Columbus leads the best-of-7 series 2-1 entering Game 4 here Thursday (7:30 p.m. ET; NBCSN, CBC, SN, TVAS).
"A couple of days ago, zero penalty minutes, well, now it's at four," Cassidy said. "Now we've got to talk to him about staying out of the box on altercations, whatever you want to call them. You're going to take penalties through the course of a game if you're competing. Marchand] will do that on pucks.
"The ones that, call them away from the play, maybe -- we've got to talk to him about those. We need him on the ice. The way this series has gone, every power play has been crucial both ways, so we've got to make sure that he plays hard between the whistles, and that will be the message to him."
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Cassidy hadn't had that conversation with Marchand by midday Wednesday but said it was on the schedule.
"My talk with Brad will happen, and it'll be quick," Cassidy said. "We've had a few."
The discussion was precipitated by an incident that occurred with 1:01 remaining in the third period of Game 3, which Columbus won 2-1. With Blue Jackets defenseman Scott Harrington down on his knees by goalie Sergei Bobrovsky, Marchand popped him in the back of the helmet.
Marchand was not penalized on the play, and the NHL determined there would be no supplemental discipline.
"Stuff like that is going to happen," Harrington said. "We're not going to make anything out of it. I think we saw that there's no suspension or anything, so it's a hockey play and it's the playoffs. That's what it's all about. You're going to take some shots. Not going to let it linger past today."
Marchand said he saw Boston forward Jake DeBrusk take a couple of punches and that his actions were a reaction to that. He said it's not a matter of frustration.
But, as he said, "It was an unnecessary play. But it is what it is. Games go on and worry about the next one."
Asked if he regretted it, Marchand said, "I guess, because having to talk about it today, it's probably not something that [I'd] go back, do it again."
For the Bruins, though, there was an important message that they felt they needed to get across to Marchand, who led them with 100 points (36 goals, 64 assists) this season but has none in the series.
They need him on the ice. Though he wasn't penalized on the play, he could have been, just when the Bruins had pulled goalie Tuukka Rask and were trying desperately to tie the game.
"We've got to keep him on the right side of the line," Cassidy said. "We've been dealing with this for a long time. This isn't an easy [fix]. This isn't just me going up, 'Hey, [Brad], knock it off.' It doesn't work that way. He's got to find it in himself to make sure."