Reirden was an assistant for the Pittsburgh Penguins from 2010-14 and coached Wilkes-Barre/Scranton in the American Hockey League for parts of two seasons from 2009-10. He interviewed for coaching jobs with the New Jersey Devils in 2015 (when John Hynes was hired) and the Calgary Flames in 2016 (when Glen Gulutzan was hired).
"He's a guy who's a very good communicator, very good specialist, and has lots of respect from us," Capitals captain Alex Ovechkin said of Reirden on June 20.
A 12th-round pick (No. 242) by the New Jersey Devils in the 1990 NHL Draft, Reirden had 46 points (11 goals, 35 assists) in 183 NHL games as a defenseman with the Edmonton Oilers, St. Louis Blues, Atlanta Thrashers and Phoenix Coyotes.
"I feel like the whole coaching staff has been doing a great job over these years to teach us whatever it is, penalty kill, 5-on-5," Capitals center Nicklas Backstrom said. "All of [the coaches have] an input on everything, which makes it probably easier for him. And he knows us too, as guys, which is going to help him."
Reirden as an assistant was primarily responsible for coaching the Capitals defensemen and power play.
"I think he did a great job taking everybody for being different people and seeing things different ways," defenseman John Carlson said. "I just think he seemed to connect with everyone's different personalities. I think he makes you look at the game a little bit differently."
The Capitals won the Stanley Cup for the first time in their 43-season history when they defeated the Vegas Golden Knights 4-3 in Game 5 of the Final on June 7. In the days afterward, Trotz and MacLellan each said they wanted Trotz to return, but the sides could not agree on a contract extension, which led to his resignation.
The last time a team repeated as Stanley Cup champions with a first-time NHL coach in the second season was in 1969, when the Montreal Canadiens won with Claude Ruel. He succeeded Toe Blake, who retired after the Canadiens won the Cup in 1968.
"In the room and in practice he's always giving little tips to everyone," forward Devante Smith-Pelly said. "I think he taught me just a lot of little things positional-wise and things like that maybe other coaches never taught me. ... He did amazing job, obviously, with the defense and a big part of the whole run. So I think he'll do a great job and definitely help us defend the Cup."