And for creating a moment he had always hoped for, always believed in.
"It was a jolt through my system," Grzelcyk said. "I didn't really know what was going on. I was trying to hide it as best I could, but the other guys were, I think, trying to make me smile. I was really happy."
He spent his childhood picturing it, imagining it happening. He would see the packed stands, the cheering, the moment. He would wish for it, dreaming it into existence.
"All the time," Grzelcyk said. "Whenever I was skating out there, I was always alone, there was no fans, but I would always kind of picture a full crowd like there was tonight."
His father wasn't quite so sure. He knew how hard this was.
"He did more than I did," John Grzelcyk said, of hoping for the moment. "I knew it was kind of unrealistic from working here all the time. It was, just go out and get an education, play hockey. 'No, dad,' he would say, 'I want to play in the NHL.' He was like 10 or 11."
Matt Grzelcyk had known his mom would be there on Friday, but didn't know his father would be as well. But John Grzelcyk was, stalking around Section 21, between the morning work getting ready for the game and the changeover for the night's Boston Celtics tip-off, as he had done so many, many times before.
This one ended differently.
As John Grzelcyk stood by the family area, waiting to get back to the job he has done for 50 years, his son approached. Matt Grzelcyk walked up to his dad and handed him the tape-wrapped puck. His father already had the puck from his other biggest goal on a crowded mantel, from the overtime winner that the Boston University product had scored to give the Terriers the 2015 title in the Beanpot, the annual tournament between BU, Boston College, Harvard and Northeastern.
But there would be room for this one, or he would make room.
"To get his first NHL goal in front of his mother and his family and all my aunts and nieces, nephews, everybody's watching," John Grzelcyk said, trailing off.
He had seen his son score where his idol had once scored. And his son had gotten to score against his own idol, with John Grzelcyk revealing that Matt had been a Sidney Crosby fan as a kid.
"And now he's playing against Sidney Crosby," John Grzelcyk said, in a bit of disbelief. "He got to play against his boyhood hero."
It was easy to marvel at how far his son had come, since those days with that crate, since those days of packed bags and free moments on the ice, pretending to score in front of all of Charlestown, all of Boston, the stands packed and the people cheering.
It had happened. He had the puck to prove it.