U.S. doubles tennis star Mike Bryan pretended to load his racket like a gun and shoot a line judge over an incorrect call ... and the guy was fined $10,000 for the gesture.
It all went down Sunday at the U.S. Open ... when Bryan challenged an "in" call during his doubles match against Federico Delbonis and Roberto Carballés Baena.
Turns out, Bryan was right to protest -- the replay showed the ball was out -- and as part of his celebration for the successful challenge, he pointed his racket at a line judge and pretended to shoot.