Smith-Pelly, who is black, was in the penalty box in the third period after a fight with Blackhawks defenseman Connor Murphy. He was seen becoming visibly upset with fans at the glass to his left, at one point grabbing his stick and walking over to tap the glass with it. United Center ushers removed four fans from the game after the incident.
A Capitals spokesperson confirmed to ESPN that the fans were chanting, "basketball, basketball, basketball!" at Smith-Pelly.
Capitals coach Barry Trotz called the incident "disgusting" and racially motivated.
"There is absolutely no place in the game of hockey or our country for racism. I think it's disgusting. There's no place for it. Athletes in our country don't deserve that. It just shows ignorance," said Trotz, who said Smith-Pelly was upset about the incident after the game.
The Blackhawks issued a statement Saturday night saying: "We were made aware of an incident at tonight's game involving a small group of attendees who made harmful comments directed at Washington Capitals player Devante Smith-Pelly. The fans were immediately removed and we apologize to Smith-Pelly and the Washington Capitals organization. We are committed to providing an inclusive environment for everyone who attends our games and these actions will never be tolerated."
On Sunday, commissioner Gary Bettman released a statement that said the NHL "condemns this unacceptable and reprehensible behavior."
"The League fully supports the actions taken by the United Center and the Blackhawks to eject the offenders and would expect the same response to any similarly unacceptable behavior at any of our arenas," the statement continued.
"While this incident was isolated in nature, no player, coach, official or fan should ever have to endure such abuse at one of our games. The League will take steps to have our clubs remind all stakeholders that they are entitled to enjoy a positive environment -- free from unacceptable, inappropriate, disruptive, inconsiderate or unruly behaviors or actions and may not engage in conduct deemed detrimental to that experience."
There are fewer than 30 black players currently on NHL rosters. Smith-Pelly debuted in 2011 and has played 319 games for the Anaheim Ducks, Montreal Canadiens, New Jersey Devils and the Capitals, whom he joined last summer. He has seven goals and nine assists in 54 games.
He told the Toronto Star in 2017 about an incident when he was playing in his first rookie tournament in Penticton, British Columbia. He was coming off the ice and heard a fan scream, "Go back to playing basketball."
Said Smith-Pelly to the Star: "I can't go to anyone on my team and have them understand really how it is to be in my shoes. Just because I'm a professional hockey player: they just don't understand. So it's really lonely in that sense. You don't really have anyone."
February is the designated month for the NHL's "Hockey Is For Everyone" promotion, which "uses the game of hockey to drive positive social change and foster more inclusive communities."