For those who are ready, that means opportunity. For Jakob Forsbacka Karlsson , that means a spot on the No. 1 line.

His defensive duos have been in flux all season, and he was regularly tinkering with his forward lines before Patrice Bergeron’s shoulder injury, trying to coax mature performances out of young players.

A coach with a healthy roster prefers to let chemistry develop with his lines and pairs. Bruce Cassidy does not have that luxury with the Bruins.

In Wednesday’s 3-2 overtime loss at Detroit, the rookie center’s promotion from third to second line preceded the opening goal. JFK scored his second in as many games at 4:08 of the second period, some 14 seconds after Cassidy sent him over the boards with Brad Marchand and Jake DeBrusk.


Friday against Pittsburgh, Cassidy promoted him again: to the top line, with Marchand and David Pastrnak. In Detroit, Cassidy said, he saw the Stockholm native skating hard, which lets him find the puck and make plays.

The JFK switch, in combination with an Anders Bjork-Colby Cave swap (more on that below), allows Cassidy to move Joakim Nordstrom to a more preferable spot: on the wing, where he can “hunt pucks.”

Cassidy said JFK “broke two or three teeth” when he deflected Dylan Larkin’s shot into his mouth. He had a dentist visit Friday morning.

“Hopefully he’s not too goofy on the ice,” said Cassidy, who recalled having a front tooth knocked out by a stick as a young player.

“Listen, they hurt,” he said.

Bjork bounced

Bjork, who started Wednesday on the top line with David Krejci and Pastrnak, was scratched Friday. In Detroit, Cassidy was not pleased with Bjork, who went minus-1 and landed one shot on net in 14:55. He pointed to Bjork’s role in the Red Wings tying the game in the third period. He forced a shot that, in combination with an ill-advised Steve Kampfer pinch, led to a 2-on-1 break the other way for a goal.


Cassidy wasn’t down on Bjork on Friday, noting that the ex-Notre Dame scorer is playing well without the puck, and that part of his offensive struggles as a pro (5-10—15 in 49 NHL games) have been injury-related. Shoulder trouble limited him to 30 games last season. His recovery extended deep into the preseason.

The Bruins view Bjork as similar to DeBrusk: fast wingers of similar size.

“Jake finds a way to get inside and get greasy goals around the net,” Cassidy said. “That’s where I think it’s going with Anders . . . play a little more on the inside, find a way to get chances at the top of the crease, and tips.

“Part of the onus is on us to make sure we keep him in the right place. Part of it is on him to push through and beat other guys out for the ice time.”

Cave called up

Cave, who played three games last season, was in the lineup with Bjork scratched. A four-year AHL veteran, Cave, 23, was leading Providence in scoring (6-12—18 in 15 games). He was centering a third line with Nordstrom (LW) and Noel Acciari (RW).

“He’s grown his offensive game,” said Cassidy, who coached him his first two seasons in Providence. “We think there’s something there.”

In a three-game call-up last spring, Cave dropped Florida star Alex Barkov with a hard hit. He has shown he can be responsible defensively. The question, Cassidy said, is if Cave can push the pace for extended periods.


“Let’s get after it,” Cassidy said. “No more nerves. You don’t know how many chances you’re going to get in this game, so don’t leave anything in the room.”

Moore returns

More encouraging news for the Bruins’ ailing defense: John Moore returned after a three-game absence with an undisclosed lower body injury. He paired with Torey Krug, who was his penalty-kill partner in the morning skate.

With Moore’s return, Kampfer was the extra defenseman.

Brandon Carlo (upper body), Cassidy said, is a maybe for Monday at Toronto. Charlie McAvoy and Urho Vaakanainen, neither of whom skated with the team Friday, are still TBD.

“My guess is Brandon would be the closest,” Cassidy said.

Return of Halak

Jaroslav Halak started after a 32-save effort last Saturday in Arizona. The Penguins of Sidney Crosby, Evgeni Malkin, Phil Kessel, etc. are a different animal than the Coyotes, whose leading scorer is Clayton Keller (5-8—13 in 20 games). But Halak was outstanding last Saturday, and aside from a few leaky goals in an off night at Colorado Nov. 14, he has given the Bruins All-Star work (2.07 GAA, .935 save percentage).

Despite their injuries, the Bruins know they must play tighter in front of him and Tuukka Rask (who gets the call Saturday in Montreal).

“I thought against Detroit, even though we got a point, the third period was not our type of hockey,” Cassidy said. “Tuukka made some real good saves. We broke down a lot. We’ve got to get out of that in a hurry, or teams are going to eat us alive offensively.


“Dallas and Arizona aren’t firepower teams like Pittsburgh, the way Montreal’s playing, and Toronto. We were mindful of that, talked a little about that this morning.

“Listen, we’re trying to do it one game at a time, and then maybe the next game, 37 [Bergeron] and 33 [Chara] are ready to play. We know that’s not happening for a while, but I think as a staff, that’s how we look at it.”

Follow Matt Porter on Twitter at @mattyports