Ducks aren’t a happy group after 3-0 loss to Stars in Game 3

DALLAS — If there’s a line of sportsmanship that shouldn’t be crossed, Ryan Getzlaf’s judgment is that you shouldn’t throw a left hook at a guy whose face is severely stitched up.

Yet, that and other unwritten rules were fudged Monday night by the Dallas Stars, whose reward of a 3-0 Game 3 victory over the Ducks at American Airlines Center probably means the hostilities and punchiness will escalate.

The Ducks’ lead in the first-round Western Conference series was cut to 2-1 with Game 4 in Texas on Wednesday night.

After Stars forward Antoine Roussel threw the left at the protective mask that covers the countless stitches Getzlaf received under his mouth after getting struck with a Dallas shot in Game 1, the Ducks are poised to stoop to whatever level it takes to win.

“It’s playoff hockey, but I think guys need to step up and play that role and do it right back to them, to their star players,” Ducks forward Patrick Maroon said after his team-best six shots on goal were denied in goalie Kari Lehtonen’s 37-save shutout.

Earlier Monday, Dallas Coach Lindy Ruff said he wanted his desperate team to play “with that amount of energy that puts us right on that line,” of being too amped up.

Getzlaf said the Ducks learned, “You’ve got to stay as disciplined as you can, but you’ve got to protect yourself, too. I never expected them to target my face that much, but that’s the way it goes, I guess.

“There’s class. You can play hard, but, me personally, if a guy’s got a bad jaw, I’m not going to hit him in the jaw. But everybody’s different. It’s going to be a war.”

Of greater concern than the scoring inability was the season-ending injury to Ducks defenseman Stephane Robidas, who fractured his right leg when Anaheim nemesis Ryan Garbutt slid and crashed into his former teammate who broke the same leg in late November.

To pour salt in the wound, Garbutt, who was suspended after an October hit on ex-Ducks forward Dustin Penner, scored 7 minutes 52 seconds into the third period, thrilling a Dallas crowd watching its first playoff home game since May 19, 2008.

“We preach about our depth, and the guys who have been sitting out for us are top-end NHL players, but the type of guy [Robidas] is, the leadership and intangibles he brought to this team, are what we’re going to miss the most,” Ducks defenseman Cam Fowler said.

On his 10th shift Monday, just 42 seconds into the second period, Robidas was downed in obvious pain, slamming his gloved right hand on the ice.

Acquired from Dallas on March 4, he returned to play March 18 for Anaheim, providing veteran poise and toughness with a goal and four assists down the stretch, playing 20 minutes-plus in 10 of 14 games.

The sellout Dallas crowd affectionately chanted “Robi!” as he was helped off the ice.

After two periods, Dallas led 2-0 despite the Ducks leading in shots, 30-15, with the Stars’ penalty total bulging to six.

The peak of Anaheim’s frustration arrived on a Ducks’ power play with less than five minutes left in the second.

Lehtonen stopped a behind-the-net pass to Maroon, watched a Corey Perry shot sail off target, then denied a Teemu Selanne shot in front.

With that, Dallas forward Valeri Nichushkin took a pass from Tyler Seguin, beat Bryan Allen toward the net and blasted a shot that scooted under Ducks rookie goalie Frederik Andersen with 2:45 left in the second.

Maroon had enough with less than six minutes left, lashing out and getting sent to the dressing room by committing a game-misconduct penalty.

“I guess you do anything to win,” Ducks Coach Bruce Boudreau said. “You can do a lot of things, take liberties, with a lead if it’s not being called.”

lance.pugmire@latimes.com

Twitter: @latimespugmire