ATLANTA — Boston Celtics forward Paul Pierce and Washington Wizards guard DeShawn Stevenson were fined $25,000 each by the NBA today for making "menacing gestures" in playoff games, another attempt by the league to crack down on bad behavior.

Pierce was sanctioned for flashing a hand gesture toward Atlanta's Al Horford and attempting to stare him down in the fourth quarter of the Celtics' 102-93 loss to the Hawks on Saturday. Pierce had to be pulled back to the Boston bench by his teammates.

Stevenson was called for a flagrant foul when he swiped LeBron James' burgundy headband off late in the first half of a 100-97 loss to the Cavaliers.

"The league is sending a message that we have the best athletes in the world: Play the game," NBA commissioner David Stern said during a stop in Atlanta. "If you get baited, don't take the bait."

After Horford hit a clinching basket with 22 seconds left in Atlanta's Game 3 victory, the rookie began jawing with Pierce before heading for the Hawks bench. Pierce followed Horford as far as midcourt, glaring in his direction before holding up his right hand, forming an "O" with his thumb and index finger and extending the other three fingers.

Pierce's gesture resembled a gang sign, though Boston general manager Danny Ainge denied that it had anything to with such an illicit activity. He said the player holds up three fingers to represent "blood, sweat and tears."

"Watch what Paul does when he's introduced. He's done it for every game," Ainge said. "That's not anything related to" gangs.

Horford said he understood why the league came down so hard on Pierce.

"I knew he was upset after the play," the Hawks forward said. "I honestly didn't know what it meant. But the league wants to keep its image."

Pierce declined comment on the fine, though he indicated it would be appealed.

"I'm here getting ready for Game 4," he said before Monday night's contest at Philips Arena. "We'll take care of that when the season's over. I'm not really worried about it right now."

Boston coach Doc Rivers expects Pierce to win the appeal.

"It's silly," Rivers said. "Unfortunately, everybody's very sensitive about signs. I didn't know that. I know now. I'll be careful when I'm giving signals to the players, I'll tell you that."

Stevenson called James "overrated" after a game in March, and turned the playoffs into a personal grudge match.

The league said Stevenson made "menacing gestures" during the first quarter of Sunday's game. In the second, he came across the lane and swiped his right arm across the top of James' head, knocking off the All-Star's headband and sending him sprawling to the court.

The image-conscious Stern said the league is serious about its crackdown.

"We've got extraordinarily gifted athletes playing a special game," he said. "We're not going to let it degenerate into something else. Period."