The pair of defensemen go back a long way, back to 1982, when they first became teammates with Ottawa of the Ontario Hockey League, when Shaw sat two seats down in a room that would become the foundation of the 1984 Memorial Cup-winning 67's, when they teamed with players like goalie Darren Pang and forward Gary Roberts, led by legendary coach Brian Kilrea.
They now stand behind opposite benches, with Cassidy coach of the Boston Bruins and Shaw an assistant to coach John Tortorella on the Blue Jackets, with the two teams playing in the Eastern Conference Second Round. The best-of-7 series is tied 1-1 heading into the Game 3 at Nationwide Arena on Tuesday (7 p.m. ET; NBCSN, CBC, SN, TVAS).
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"The hockey world seems big, but when you really boil it down it's a pretty small world, so you keep coming across the same faces," Shaw said. "We have so many good memories because of what we went through as a team, what we accomplished."
In a recent press conference, Cassidy used the word idol to describe Shaw, perhaps an overstatement, as he later clarified that his hockey idols were defensemen like Bobby Orr and Ray Bourque. But for him, Shaw was also an idol, if a more real, tangible one.
The year before he joined the 67's, Cassidy was playing an hour outside Ottawa. He would go to the OHL games when he went home on weekends, and he watched Shaw play. He saw similarities to himself and his game, and he took note of what he could.
"He was my size-ish, offensive guy, puck mover," Cassidy said. "Back then, smaller defensemen -- we were considered small at 6-feet [Shaw] or 5-11, 185 pounds [Cassidy]. I like the way he played, controlled the pace of the game, good passes, power-play guy. And still seemed like he didn't want to get scored on as well."
The next year, they became teammates. They reflected each other, both quiet, in a room dominated by talkers like Pang and Roberts. Shaw and Cassidy sat back. They observed.
"I always really looked up to him," said Cassidy, who sees a comparison between Shaw and current Bruins defenseman Matt Grzelcyk. "He would always give me the puck. He would carry it up the ice. He was the guy who always took it in. I was more the shooter or make the last play to the net as a defenseman. And I always appreciated that.
"He didn't say much. If he had something to say, he said it, but he was a good, positive guy. Good teammate."