According to a release by the league, Nurse threw his mask toward the stands and directed profanity at referees before leaving the court (h/t Marc Stein of the New York Times).
Utah went to the line 41 times compared to 14 trips for Toronto in the three-point win, which came down to a pair of free throws by Utah's Mike Conley.
The difference at the line was the second-largest of the season, according to Chris Black of Sportsnet. To Nurse, it was also why the Raptors lost.
"A lot of calls, man," Nurse said, per Arun Srinivasan of Yahoo. "Every possession was free throws. We were twice the aggressor."
While complaints about inconsistent referees are a problem that every team runs into throughout the season, the incident with the mask comes as Toronto is working its way back from a run-in with COVID-19.
Shams Charania of The Athletic and Stadium reported on March 3 that "many" of the seven positive tests reported by the league in the last week of February were among the Raptors, and he cited sources that suggested spread among the team stemmed from "inconsistent mask-wearing" from coaches.
Nurse, who said in January that he needed to step up his adherence to the league's mask-wearing guidelines, refuted that report on March 10.
"I think that I don't think anybody would have any idea what they're talking about, saying that," he said (h/t Aaron Rose of Sports Illustrated. "That is a really unfair, very speculative thing to say, unless you have video evidence of it, because I don't think it's very cool to say that."
The Raptors are in the midst of a seven-game losing streak that they will look to end on Sunday against the Cleveland Cavaliers.