Novak Djokovic, the top-seeded men’s tennis player in this year’s U.S. Open, has been disqualified after accidentally hitting a line judge with a ball during his match.

The incident happened during Djokovic’s fourth-round match against Pablo Carreno Busta on Sunday. Djokovic was heavily favored to win the tennis tournament, as he was off to a perfect 26-0 start this season.

During the first set, Carreno Busta was up 6-5 on Djokovic, who walked to the sideline during the changeover between sides and hit a tennis ball behind him. The ball struck a female line judge who fell to her knees in the back of the court and clutched her throat. In a clip posted by ESPN, the tennis star looked back in shock as he realized his accident and walked over to the line judge to tend to her.

Two officials met with Djokovic near the net, dismissing him from the tournament.

The United States Tennis Association issued a statement on the incident, explaining that Djokovic’s actions fall within the rules of disqualification.

“In accordance with the Grand Slam rulebook, following his actions of intentionally hitting a ball dangerously or recklessly within the court or hitting a ball with negligent disregard of the consequences, the U.S. Open tournament referee default Djokovic from the 2020 U.S. Open,” the statement read. “Because he was defaulted, Djokovic will lose all ranking points he earned at the U.S. Open and will be fined the prize money he won at the tournament in addition to any or all fines levied with respect to the offending incident.”