World number one Novak Djokovic has lost his fourth round match in the US Open after he was disqualified for striking a female line judge in the throat. 

Djokovic had just had his serve broken by Pablo Carreno Busta to trail 5-6 in the first set. 

Walking to the sideline at the change of ends, a frustrated Djokovic dramatically hit a ball behind him without looking forcing the line judge to her knees as she held her neck in pain.

The tennis champion discussed the incident with officials including tournament referee Soeren Friemel, before accepting the decision and shaking Carreno Busta’s hands as he walked off court.

It was an unexpected end to Djokovic’s 18th Grand Slam title and his unbeaten start to 2020.

Before the incident occurred, the Serbian athlete had a match record of 26-0 for the season.

“I was a little bit in shock, no?” Carreno Busta said later at a news conference done via video conference.

Asked whether Djokovic should have been allowed to continue to play, Carreno Busta shrugged and replied: “Well, the rules are the rules … The referee and the supervisor (did) the right thing, but it's not easy to do it.”

Djokovic did not speak to the media.

The USTA released a statement after the incident.

“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 statement read.

“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 levied with respect to the offending incident.”

Despite Djokovic not intending to hit the line judge, he was defaulted due to hitting a ball out of anger.

This article originally appeared on Over60.