According to Isabelle Khurshudyan of the Washington Post, a Caps spokesman said the fans yelled "basketball, basketball, basketball" at Smith-Pelly while he was in the penalty box.
Capitals head coach Barry Trotz took issue with the fans after the game, as seen in this video courtesy of NBC Sports Washington's Tarik El-Bashir:
Trotz called the taunts "disgusting."
The Blackhawks released the following statement and apologized to Smith-Pelly, per Mark Lazerus of the Chicago Sun-Times, and the NHL also released a statement (h/t ESPN.com's Greg Wyshynski):
The 25-year-old Smith-Pelly, who is black, is in the midst of his first season with the Caps.
Saturday's incident occurred after Smith-Pelly was assessed a five-minute penalty for fighting Blackhawks defenseman Connor Murphy.
On Thursday, Smith-Pelly squirted a heckling fan with his water bottle while in the penalty box during a 5-2 win over the Minnesota Wild.
In 54 games this season, Smith-Pelly has seven goals and nine assists for 16 points.