Montreal's defenders take the majority of the heat when discussing the Habs' weakness on defense, however often it's the forwards who are failing on their assignments. This leads to incredibly easy goals for their opponents.
This play got off to an innocent start. Max Pacioretty chipped a puck across the offensive zone, forcing David Desharnais to chase. Desharnais gets out-muscled fairly easily, and loses the puck. The rush is on.
The Penguins took advantage of two mistakes during this part of the play. First off, Beaulieu made a weak swat at the puck, which barely slowed them down. Beaulieu then failed to close the gap, which gave the Penguins a free ride into Montreal's defensive zone. If Steve Downie was a vampire (and I'm not necessarily convinced he isn't), he'd be allowed in the home, because he was definitely invited in.
Despite allowing the Penguins to enter the zone without any resistance, the Habs seem to have the situation under control, as Max Pacioretty dropped down low to cover David Desharnais, who hasn't managed to make it back into Montreal's defensive zone yet. P.A. Parenteau has Beau Bennett covered, Tom Gilbert has his man covered, and Nathan Beaulieu is on his way back into the slot. What could go wrong?
A failed check by P.A. Parenteau, a weak poke attempt by Max Pacioretty, and some unhealthy puck watching by Nathan Beaulieu quickly turns this innocuous play into a legitimate problem. Bennett shows off some good hand-eye coordination to keep possession, as well as a decent dose of puck luck.
What does that lead to? Great things for the Penguins. Bennett, who had yet to hit the score sheet until he faced the Canadiens, finds a wide open Kris Letang. No seriously, wide open might be an understatement. Absolutely no one is covering the point, and Letang knows exactly what to do.
This is what four failed defensive assignments looks like in a still frame. As we can see from this angle, David Desharnais was playing the role of the breakout man, but considering Montreal didn't possess the puck, he definitely needed to adjust his positioning to at least cover Letang. Max Pacioretty should have stayed down the middle as well.
For some reason, even though all three players failed on their defensive coverage of Beau Bennett, they stayed bunched up and continue to puck watch. Steve Downie on the other hand, identifies the absolute lack of coverage, and streaks towards the net.
Kris Letang could probably make this pass even if the Habs had put together something resembling reasonable coverage. It's worth noting that the only player on the ice that didn't completely flunk his defensive coverage was Tom GIlbert, who kept a close eye on Sutter throughout the play.
A lot went wrong during this play: lazy backchecking, poor defensive coverage, weak check attempts & puck watching. It was very Buffalo Sabres in its application, and not something you want to see from a team's "first line," especially when they're not facing a line featuring either Evgeni Malkin or Sidney Crosby.
It goes to show that even though defensemen almost always get the blame in defensive breakdown situations, generally the forwards should share a fair amount of the blame.
This isn't a new phenomenon for the Canadiens, who have a long history of forcing their defenders to win battles and find them with 100 foot passes. When they fail to do so, the defenders receive criticism, but in reality it's a forced play that leads easy goals for the opposition, and there's not much defenders can do to stop it when things go wrong, as evidenced above.