Capitals Justin Williams, left, and John Carlson work a crossword puzzle together in the trainer's room at Kettler Iceplex. (na/Courtesy of the Washington Capitals)

Nate Schmidt saw the unattended crossword puzzle and instantly knew who it belonged to. Jack Hillen peppered him with questions from crosswords every morning, so as Schmidt scanned the clues, he figured writing in an answer was harmless. Then he got an earful from Hillen.

“He lost it on me,” Schmidt said. “Thought it was the worst thing I could’ve done.”

More than a year after that incident, Hillen said Schmidt was “probably exaggerating,” but added that Schmidt should’ve known better. Professional hockey is riddled with crossword enthusiasts, players looking for a good way to pass their free time. For the first-place Washington Capitals, completing crosswords is a daily routine, perfect for team bonding while also keeping their minds active.

“It’s a cult of crossword men,” Schmidt said. “Keep the mind sharp is what I say. That’s one way guys do it. It also kind of takes your mind away from hockey, but also keeps it mentally engaged and in the moment. You’ve got to get away from the game every once in a while, but you don’t want to completely shut off.”

Goaltender Braden Holtby said crosswords have been around hockey “for 50 years, or more.” When Hillen, a former Capitals defenseman, was just starting his career with the New York Islanders in the 2008-09 season, he was still a fringe player, living out of a hotel while splitting time between the NHL and American Hockey League. There were always free USA Today newspapers in his hotel, so he started doing the Sudoku puzzles in them. Teammate Doug Weight then convinced him to try the crossword instead and it quickly became an addiction, something he looked forward to when he woke up in the morning.

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On the Capitals, he was one of only a handful of players who worked on a crossword while sitting in the cold tub or eating breakfast. Usually, it was just him and massage therapist Curt Millar. Told that the Capitals now have at least six players who work on crossword puzzles in the morning, Hillen jokingly called them “hypocrites.”

“Everyone would kind of would poke fun at him for doing it,” defenseman Karl Alzner said.

“They tried to mess me up a few times by writing in the wrong answer,” Hillen said.

[The Post’s daily crossword puzzle]

Hillen’s addiction spread. The current regulars of Washington’s crossword club are Holtby, John Carlson, Justin Williams, Karl Alzner and T.J. Oshie. Nicklas Backstrom, Marcus Johansson and Schmidt occasionally chip in answers, though Schmidt now always asks for permission before writing on someone else’s crossword.

“Trainers are a big help,” Holtby said. “They’re the ones that are smart.”

Players will either grab a free newspaper from the hotel lobby, or they’ll just print out a crossword. Backstrom used to tease the players who worked on them daily, then he started working on one regularly with Holtby. With English being the Swede’s second language, being able to navigate the word play in the clues is an impressive feat.

Capitals defenseman Karl Alzner uses a crossword as a distraction while getting treatment at the team's Kettler Iceplex. Alzner does the Post’s crossword because, he said, “that’s the paper I subscribe to.” (na/Courtesy of the Washington Capitals)

“I only ask them if there’s a simple one for me,” he said.

The Capitals’ offseason additions of Williams and Oshie have given them a boost on the ice, but Washington also gained two experienced crossworders. Both said their past teams also had crossword clubs, with players pulling them out on short bus rides to the rink. Carlson used to be the team’s best crossworder, but the consensus is that it’s now Williams, with Carlson a close second.

“We got a lot of young pups on this team, you know?” Williams said. “I’m like the father-figure of the crossword. I’ve been doing it a little longer, so I know some answers that maybe they don’t.”

Williams is the cleanup hitter of the crossword club. He’ll work on his own, able to complete a New York Times crossword on a Monday or Tuesday, but when others get stumped, he’ll help them finish. Alzner said it’s like having a computer next to you.

Once a player working alone gets stumped, he will gravitate toward pairs; Alzner and Oshie work together, as do Williams and Carlson. Outside of giving answers, the process is silent. They use a pen, and when they finish, everyone who contributed signs the bottom.

“I like to run through all of the questions and just walk away, and then come back and try to read them again,” Schmidt said. “That way it makes me look smart. Like, ‘Oh by the way, 17 down, that’s turtle.’ Then walk away.”

Before crosswords, some Capitals would play brain-training games on Lumosity.com or work on Sudoku puzzles. Oshie likes it because it’s a group activity over breakfast, something that brings teammates together. Williams said he prefers puzzles to staring at his phone. Other players see it as a way to expand their interests beyond just hockey.

“With hockey, you don’t learn a lot of stuff outside of the game,” Holtby said. “Any way you can do that, be it crosswords, reading, documentaries or whatever, you just try to keep your mind sharp in other ways because a hockey career ends sometime and you’ve just got to prepare and keep your mind sharp when you have to use it again.”

Of course, there’s some kind of competition involved.

“We kind of have a running joke that anyone who can finish the Sunday New York Times gets a couple hundred bucks,” Alzner said. “No one’s been able to do it, but that’s the end game.”