BOSTON -- Gagging from noxious fumes as they evacuated their bench, the Boston Celtics' thoughts turned to terrorism. Coach Jim O'Brien lobbied for the game to be stopped.

	J.R. Bremer, right, and his teammates had a tough time breathing Friday.

But NBA officials, working with Boston police and FleetCenter security, decided that the substance sickening the players and the fans sitting behind them was most likely Mace or pepper spray released as a prank.

"It is a sick prank,'' FleetCenter chief Richard Krezwick said Saturday before the building hosted an NHL game between the Boston Bruins and the Washington Capitals. "In this day and age, people like that have to be punished.''

The third quarter of their game against the Los Angeles Clippers had just ended on Friday night when the Celtics suddenly fled their bench, covering their faces with their warmup jackets or towels. During the nine-minute delay, O'Brien could be heard trying to persuade referee Hue Hollins to postpone or cancel the rest of the game.

"We have directives we have to follow in situations like this,'' Hollins told a pool reporter after the game. "We can't just arbitrarily say the game was over.''

NBA vice president Stu Jackson said Hollins followed the procedure established to protect the safety of the teams. Because an NBA referee can't be expected to assess a threat, the league assigns a security representative to each city as a liaison to local law enforcement.

"It's the crew chief's decision whether to continue the game or not,'' Jackson said. "But he is not operating alone. The procedure is to operate with security.''

Asked whether the system has been changed to account for the increased -- but still unlikely -- possibility of terrorist threats, Jackson said, "We've had the procedure in place for a long time. But we're obviously more in tune with it now.''

Krezwick said security, including a Boston police officer trained in hazardous materials, determined that the quickly dissipating fumes were not likely to pose a danger and the game could continue.

"That is how you proceed, rather than creating larger issues with a mass exit,'' FleetCenter general manager John Wentzell said.

No one required medical treatment, police said.

Security at sporting events has come under scrutiny before. In September, police trying to break up a fight in the stands at a game between the Philadelphia Eagles and Washington Redskins used pepper spray, which drifted onto the field and made some players sick.

But Friday night's situation also brought back memories of more dangerous security breaches, like the stabbing of Monica Seles by a German tennis fan or the on-field beating of Kansas City Royals first base coach Tom Gamboa by Chicago White Sox fans.

For many of the Celtics, their first thought was terrorism.

"With what's going on in the world, we're obviously going to be very cautious,'' Celtics forward Antoine Walker said.

Asked whether he was concerned the fumes might be related to an attack, O'Brien said, "Of course.''

But all involved became convinced that what happened was meant as a prank.

"It was a very ill-timed and inappropriate prank, given the day and age we're in,'' Wentzell said.

Fans entering the building are subject to random checks with detector wands, handbags are checked and larger bags are banned. No security was added for Saturday's NHL game.

Krezwick said the city police have been sent a videotape that shows fans in the area acting suspiciously before those nearby began having trouble breathing. Paul Johnson, the NBA's security official assigned to Boston, said witnesses reported four men left quickly right before the complaints began.

"We're literally and figuratively looking at the video from all the angles,'' Wentzell said.

Investigators tested the air in the arena before Saturday's hockey game and tested for any residue of the substance. No canister was found, Wentzell said.