Summarize and humanize this content to 2000 words in 6 paragraphs in EnglishANAHEIM, Calif. — On occasion, Casey Mittelstadt retreats into the defensive zone, identifies his nearest opponent, gets in his face and follows him closely. Mittelstadt then reminds himself he no longer plays for the Colorado Avalanche, who use man-to-man defensive coverage. The Boston Bruins prefer zone.That moment of indecision can be enough for whoever the Bruins are playing to exploit Mittelstadt’s hesitation.“Once in a while, he catches himself chasing people back toward the net or chasing a guy up top as opposed to handing him off,” interim coach Joe Sacco said. “Those are the only things we have to remind him of once in a while.”Playing 81 games over two seasons for the Avalanche has baked in habits that will require time for Mittlestadt to correct. As a center for the Bruins, there are more literal and figurative layers for Mittelstadt to master.The D-zone concept the Bruins practice is one that emphasizes multiple perimeters of protection. The center plays a critical role. He is required to be a board-to-board presence to support the wings. Down low, the center needs to help out the defensemen and make himself available for quick outs.The point of all this is that when a defensive breakdown occurs, the Bruins should have help nearby before the puck enters high-danger ice. Mittelstadt, an offensive-minded center, is trying to adjust.“It’s pretty different,” Mittelstadt said. “At the same time, I think it’s been all right. It fits me well, the way we want to play. I like to be able to sit in the middle of the ice, see the puck and make reads. Personally, once I figure it out and get used to it, it’s going to be a really good fit.”The Bruins traded Charlie Coyle, their best two-way center, to change their look in the middle. Mittelstadt is younger, quicker and more creative with the puck.In Wednesday’s 6-2 loss to the Anaheim Ducks, Mittelstadt centered Marat Khusnutdinov and David Pastrnak on the No. 1 line, just like he had for the first time as a Bruin in their 7-2 beatdown by the Los Angeles Kings the previous game. The nine games remaining will be a good opportunity for Mittelstadt to make his case to be Pastrnak’s first-line center in 2025-26.“He’s a pass-first player, as we know,” Sacco said. “We’re hoping it just creates some more opportunities for David to put himself in the scoring zones we want to see him in, be ready to shoot and not be looking to pass it off to someone. David’s a scorer for us.”On the power play, a left-shot setup center like Mittelstadt is usually stationed on the right-side half-wall. But for now, the Bruins are running Pastrnak on his strong side and Morgan Geekie at the left elbow.So Mittelstadt has worked the goal line, previously occupied by Brad Marchand. The former captain excels at hunting pucks, which is an important part of goal-line duty. This is not necessarily Mittlestadt’s strength. But he has enough skill to distribute from down low and execute close-quarters plays.“He can play elbow or goal line. He can move into either spot,” Sacco said. “For us right now, we feel like with Pasta playing on his forehand side on the elbow, (Mittelstadt’s) ability to work the goal line and hopefully attack down low a little bit more and run some low plays off the goal line, that will benefit him.”Mittelstadt is the Bruins’ most-skilled center. But one of the reasons Pavel Zacha (19:15) and Elias Lindholm (18:09) are averaging more ice time per game than Mittelstadt (17:28) is that they have gained the staff’s trust in defensive situations. They’re better checkers than Mittelstadt, and they have more reps in the Bruins’ system.Case in point: Mittelstadt was on the ice for five of Anaheim’s six goals Wednesday. They weren’t all because of his defensive shortcomings. But if Mittelstadt is going to get a run with Pastrnak next season, he will have to face not just shutdown defensemen but first and second lines. Whether it’s Sacco or someone else, the Bruins’ coach in 2025-26 will have to be confident that Mittelstadt can hold his defensive ground if he wants top-line action.Otherwise, general manager Don Sweeney will have to place the acquisition of a No. 1 center atop his offseason list. It went sideways last summer when he signed Lindholm, ideally a third-line pivot, for No. 1 dough and term. Sweeney cannot afford to err again.(Photo: Winslow Townson / Imagn Images)