Kawhi Leonard's mother reached her boiling point at the Spurs game Thursday night -- going off on a heckler ... calling him an "asshole" and telling him to "shut up."
It all went down in San Antonio -- where her NBA superstar son returned for the first time with his new team the Toronto Raptors.
The fans were ruthless to Kawhi during the game, chanting "traitor" and booing him almost every time he touched the ball.
At least one heckler recognized Kawhi's mother, Kim -- wearing a Leonard jersey -- and started running his mouth.