Fionn Crimmins was in the emergency room at Children’s National Medical Center for about six hours Tuesday night with a fever related to his chemotherapy. To pass the time, the precocious 5-year-old composed a song about the Maryland men’s lacrosse team set to the tune of Mark Ronson and Bruno Mars’s “Uptown Funk.”

Like most good fight songs, the words are easy to remember.

“It’s a lot of just mixing the words ‘Terps,’ ‘Terps are the best’ and ‘Go Terps,’ ” said Fionn’s dad, Conor Crimmins, who secretly recorded part of the episode and dutifully pretended to transcribe the lyrics, only to be busted when he was asked to recite them back and introduced a word that Fionn didn’t sing. “There are certain players that he’s gotten to know their numbers, so he calls out 44, which is Pat Young. There are a couple of refrains about number one Matt Rambo, who Fionn has called Matt Rainbow for the longest time.”

Fionn was diagnosed with Acute Lymphoblastic Leukemia, the most common type of cancer in children, in June 2014. He’s been an honorary member of the Final Four-bound Maryland men’s lacrosse team since October, when he was introduced to the Terps through Team Impact, a Massachusetts-based non-profit organization that matches children facing life-threatening and chronic illnesses with local college athletic teams.

“There’s definitely a reverse effect with him,” Maryland senior captain Bryan Cole told The Diamondback in February. “We’re trying to pick him up and keep his spirits up, but at the same time, when he comes in the locker room, when he’s on the field … it just makes us tremendously happy and definitely gives us a different perspective when we’re playing the game.”

In the seven months since Fionn attended Maryland’s fall scrimmage against Bucknell, he’s gone bowling with Maryland players Isaiah Davis-Allen, Dan Morris and  Louis Dubick, chased balls on the field during warm-ups, spent time with the team in the locker room and received a call from Maryland Coach John Tillman while the Terps were on the road. Fionn’s favorite part of getting to know the Terps through the Team Impact experience?

“Sometimes I get to stand on the sidelines with them,” he said.

“Everything that he talks about now is lacrosse,” Conor Crimmins said. “He’s playing lacrosse and he’s loving it, but ‘his team’ is honestly what he talks about day and night. He talks about his teammates and Coach Tillman and [Maryland director of lacrosse operations Todd MacFarlane]. He’s got a Terps flag with Testudo that hangs on the house. I can’t say enough about them. They’re just great people and they’re great guys.”

Fionn, who has another year of treatment ahead of him, started losing his hair — again — in early May. Before Maryland played Syracuse in the NCAA quarterfinals last Saturday, Tillman and almost every one of his players cut their hair in a show of solidarity for their youngest teammate.

“When we got the picture of all the guys, we were just completely flabbergasted,” Casey Crimmins, Fionn’s mom, said. “We never expected that sort of response and it’s just really, really sweet. It touched us a lot.”

Casey, who, like her husband, had no connection to the University of Maryland and knew very little about lacrosse before Fionn was matched with the Terps, received a call from Dubick last week. The freshman attackman and former Churchill High standout is one of the players who has formed an especially close bond with Fionn, even bringing pints of ice cream to the Crimminses’ Kensington home for an impromptu visit before the season. Dubick wanted to know if Fionn wanted to watch him get his head shaved by Davis-Allen on FaceTime. Of course he did.

“They’ve definitely gone out of their way to make Fionn feel like he’s part of the family,” Casey Crimmins said. “We feel that and Fionn feels that, that we’re part of the family. This is not just some pretend thing to him. He’s part of this team. He has to be there for this championship game.”

On Saturday morning, the Crimminses will drive to Philadelphia, where Maryland will play Brown in the semifinals at Lincoln Financial Field. Fionn, who predicted another Terps win, already has his outfit picked out: Under Armour Maryland shorts, a Maryland lacrosse T-shirt and knee-high socks. Win or lose, the Crimminses will return home Saturday night because they’re hosting Fionn’s sixth birthday party, which will feature a moon bounce, on Sunday. If Maryland advances to Monday’s championship game, they’ll return to Philadelphia, perhaps singing “Uptown Terp” along the way.

“It’s just been a really, really wonderful experience for us and for Fionn,” Casey Crimmins said. “I’m very grateful for it.”