Defending US Open champion Novak Djokovic saw his run in this year’s tournament come to an abrupt end Sunday night when he was forced to retire from his match with Stan Wawrinka due to a left shoulder injury.

Then he was booed by fans inside Arthur Ashe Stadium, which was ridiculous and classless.

This all happened three games into the third set after Djokovic had dropped the first two sets by scores of 6-4 and 7-5.

The Wimbledon champ had been bothered by a shoulder injury during the tournament and it finally became too much for him as he retired down 2-1 in the third.

Then, for some reason, fans booed him, much to the chagrin of John McEnroe, who was calling the match for ESPN:

Defending US Open champion Novak Djokovic, who was battling a left shoulder injury, retires in the third set of his match with Stan Wawrinka. Wawrinka advances to the quarterfinals. #USOpen pic.twitter.com/WXbhxo712E — ESPN (@espn) September 2, 2019

After retiring against Stan Wawrinka Novak Djokovic is booed by tennis fans in New York at Arthur Ashe Stadium. Harsh. #USOpen pic.twitter.com/kakrRWm2Q7 — Omar Moore (@thepopcornreel) September 2, 2019

Novak Djokovic booed as he leaves the court and gives the crowd a sarcastic thumbs up on his way out. — George Bellshaw (@BellshawGeorge) September 2, 2019

Just brutal stuff.

Tennis fans on Twitter were rightly upset with the fans:

It’s pretty pathetic to boo a player for retiring when he’s clearly injured, struggling, and probably not wanting to make it worse. — Michelle R. Martinelli (@MMartinelli4) September 2, 2019

Novak djokovic played beautifuly and did his best, he faced a hater while practicing and now being booed off court? Disrespectful spectators. #USOpen You did good @DjokerNole , youll always be number one in my heart man. — Michael Bullion (@drakelcrow8) September 2, 2019

I thought that #Wimbledon crowd is the worst, boy was i wrong. Imagine having to retire due to pain at the Grand Slam and after everything you brought to tennis and still will, you are being booed. I know how you feel. But please, don't. They don't deserve it. @DjokerNole 💪💪 pic.twitter.com/BOrhbnHqTa — #AlwaysProudOfNovak (@Slavica_NoleFam) September 2, 2019

Novak Djokovic didn’t deserve to be booed… he was injured like wtf get off his back — Gema Santoyo (@SantoyoGema) September 2, 2019

The New York crowd booing Daniil Medvedev is one thing. But booing a three time @usopen champion in Novak Djokovic, who has been dealing with a shoulder injury, is NOT COOL. But hey, this is the same crowd that booed Naomi Osaka. #USOpen #USOpen2019 🎾 — Lukas Weese (@Weesesports) September 2, 2019

A challenge for the vile individuals who booed Novak Djokovic for retiring with injury tonight: Try to carry out your sedentary day jobs with the injury he has. Bet 90% would fail. Yet Novak had to be ACTIVE with an injury. And you boo him. No words. 😶#USOpen — JUSTIN FREDERIC (@justinfrederic) September 2, 2019

That was disgusting by the crowd. No player should be booed off of the court because of an injury. It’s not their call to determine whether or not he should have finished the match. Ungrateful and sad from that crowd. — Jacob Kisamore (@mr_irrelevantJK) September 2, 2019