NBA executive vice president of basketball operations Kiki VanDeWeghe said in a statement Monday that Smart was fined "for aggressively pursuing an opponent in an attempt to escalate a physical altercation and failing to leave the court in a timely manner following his ejection" Saturday night.
Minutes after he was called for his first technical following his fourth foul about three minutes into the third quarter Saturday night in Atlanta, Smart was ejected following an altercation with the Hawks' DeAndre' Bembry.
Smart and Bembry had to be separated after an exchange of words as players lined up for a jump ball. After being restrained by teammates and coaches, Smart broke free and charged toward Bembry before being restrained again.
Bembry also was called for a technical foul following a video review.
Smart did not talk with reporters after the game.
"He lost his cool after the ref told him he's ejected," Bembry said. "I think after that he just thought he had nothing else to lose."
Bembry said it wasn't unusual to see Smart lose control.
The Associated Press contributed to this report.