Boston Celtics forward Glen Davis was fined $25,000 by the NBA on Thursday for shouting an obscenity to a heckling fan during Wednesday night's loss to the Detroit Pistons at The Palace of Auburn Hills.
"I don't think it's a huge step backwards [in Davis' maturity], but it is a step backwards," Celtics coach Doc Rivers said Thursday in an interview on Boston sports radio station WEEI. "Glen Davis has to grow up."
The jeering fan near the Celtics' bench repeatedly called the 24-year-old Davis "fat boy" and told him to lose some weight. Davis' response was audible on both the Boston radio and television broadcasts of the game and prompted the fan, according to a report in The Boston Globe, to file a complaint with NBA security.
The Globe also reported that the fan, Scott Zack, had been warned earlier about his heckling of Davis.
"We know what happened, and that's unacceptable," Rivers said. "It's tough when the fans are yelling that stuff at you, but you have to be stronger than that."
Davis apologized late Wednesday night in a message posted to his Twitter page.
"I'm a tough competitor and I'm proud of the work I've done to get in shape and be at the top of my game," his apology read. "That said, I shouldn't have said what I did. My apologies to the fans and my teammates."
Davis was fined by the team earlier this season for an off-court altercation that ended with Davis fracturing his right thumb and missing the first 27 games of the season. Davis also offered to pay part of a fine incurred by Rivers for a flagrant foul call on Davis earlier this month that resulted in the coach's ejection.
Rivers admitted he didn't hear exactly what the fan was screaming Wednesday night, but believed a verbal confrontation was avoidable.
"It's common sense, when a fan is yelling and it's offending the people around him, then the guy will be removed," Rivers told WEEI. "If a player points or coach points to security, there's a very good chance that person will be removed."
Rivers admitted that Detroit is one of the toughest arenas to play in given the crowd and, while he was glad it didn't escalate to any sort of physical confrontation like the 2004 brawl that occurred at The Palace, he was disappointed Davis got verbally involved.
"I've heard some vile things [said] to me and to players -- it's amazing what you hear," Rivers said. "You should turn around, point to security and let them deal with it."
Rivers then pointed to the Martin Luther King Jr. holiday earlier this week, noting: "This is what he heard and how many times he turned his cheek -- if he can do it, why can't we do it on a basketball court?"
Davis' fine was announced Thursday by NBA executive vice president of basketball operations Stu Jackson. The incident occurred with 8:44 remaining in the second quarter of Wednesday's game.
Chris Forsberg covers the Celtics for ESPNBoston.com. Follow him on Twitter.