ESPN's Adrian Wojnarowski reported Smart's fine Thursday, and Boston.com said the NBA confirmed as much shortly after:
Smart fouled out of the 129-120 loss in overtime and had to be restrained by two members of the Celtics coaching staff while shouting at referee John Goble. He told reporters Wednesday that he was yet to hear from the NBA and was in the lineup for the Celtics' 112-106 win over the Cleveland Cavaliers.
The Celtics led Brooklyn by three points with 0.2 seconds remaining when Smart was called for a foul on Caris LeVert, who knocked down all three free throws to send the game into overtime.
NBA executive vice president of basketball operations Kiki VanDeWeghe said the fine amount was a result of "multiple prior violations of acceptable on-court decorum."
VanDeWeghe noting Smart's history in announcing the fine makes it likely a more severe punishment—perhaps even a suspension—would come in the event of another incident.