World No.1 Novak Djokovic defaulted from the US Open, Sunday, after inadvertently striking a line judge with the tennis ball during his fourth-round match. Djokovic was heavily favored to win the tournament.

Novak Djokovic, US OpenAl Bello / Getty Images

While behind 6-5 in the first set against Pablo Carreno Busta, Djokovic whacked a ball away from himself in frustration, accidentally hitting a line judge in the throat with the ball. The linesperson collapsed to the ground, where they stayed for several minutes. Officials informed Djokovic that, in accordance with the rules, he would have to default from the tournament. He had previously received a code violation for similarly slamming a ball into the side of the court.

“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 US Open tournament referee defaulted Novak Djokovic from the 2020 US Open,” the United States Tennis Association said Sunday in a statement. “Because he was defaulted, Djokovic will lose all ranking points earned at the US Open and will be fined the prize money won at the tournament in addition to any or all fines leveled with respect to the offending incident.”

Djokovic, 33, was undefeated in his 26 matches this year.