The No. 1 ranked men’s tennis star Novak Djokovic was forced to default at the U.S. Open on Sunday after hitting a line judge with a ball.

The three-time tournament champion accidentally the judge in a fit of anger during his fourth-round match against Pablo Carreno Busta. Djokovic was down 5-6 when he took a medical timeout for his shoulder, then returned only to lose the game.

It seems he then smacked a ball out of frustration, which hit a linesperson, according to the tournament’s website.

Djokovic was the No. 1 seed to win the men’s tournament. His disqualification Sunday ensured that the U.S .Open is would have a first-time Grand Slam champion in men’s singles for the first time since 2014, the US Open website said.