Grant Williams of the Boston Celtics did a pretty dumb thing during Saturday's NBA Finals rematch against the Golden State Warriors, and now he has to get out his wallet and pay the price.

The NBA announced on Monday that Williams is being fined $20,000 for punching the ball into the crowd near the end of the game.

It happened with just under two minutes left in the fourth, and the Celtics down 118-101 to the team they lost to in the 2021-2022 NBA Finals. Interim head coach Joe Mazzulla called a time out, and that's when Williams punched the loose ball, which had rebounded to him after bouncing off the backboard.

Longtime referee Scott Foster, who was standing nearby, immediately issued a technical foul and ejected Williams from the game. Williams initially looked confused about why he was being ejected, but Foster appeared to explain to him on the sideline that the NBA has a rule about throwing or kicking a ball into the crowd, and breaking that rule means immediate ejection.

The Celtics weren't able to turn things around in the final minutes of the game and lost 123-107. Their next game is on Monday night against the Los Angeles Lakers.