Novak Djokovic, throughout his entire career, has been a polarising figure.

Often playing with a chip on his shoulder, at times his frustration has been warranted.

After all, he burst onto the scene as the unwanted third superstar seeking to crash Rafael Nadal and Roger Federer’s duopoly, and ironically has gone on to surpass them both in almost every tournament possible.

Always feeling like the outsider, and never afraid to give his open and honest opinion, it has won him an inordinate number of loyal fans.

Novak Djokovic facepalms as he retires injury from the US OpenPhoto credit should read DON EMMERT/AFP via Getty Images

However, it has also made him a pariah at times, with Novak Djokovic often thriving in the role of pantomime villain.

In 2019, though, the US Open crowd’s reaction took things a step too far.

Why Novak Djokovic was booed at the 2019 US Open

Djokovic has always had a complicated relationship with fans in New York, as a unique atmosphere unlike any other on tour.

There, supporters will chat, chant and shout without fear of the players’ welfare, making for a hostile and troublesome environment for most players to play in.

Naturally, the Serbian has adapted over the years and won four titles to prove that.

However, 2019 was not one of those occasions, as he was forced to retire mid-match due to a persisting shoulder injury that he simply could not shake.

He did all he could, but in the end had to concede to Stan Wawrinka in just the fourth round.

This decision was met by a chorus of boos from the US Open crowd, unhappy that their viewing had been cut short.

Martina Navratilova would then jump to Djokovic’s defence.

How Martina Navratilova reacted to US Open crowd’s treatment of Novak Djokovic in 2019

Speaking on Tennis Channel in the aftermath, she did not hold back in her scathing assessment of those supporters who chose to boo.

The 18-time Grand Slam champion hit back, stating: “You know, tennis players 365 days in a year, you play maybe 70 matches, so in 290 days you are preparing for those matches.

“So, for people to question Novak Djokovic’s commitment to the game when he defaulted yesterday and booing him when he is walking off the court… that’s just not on.

Martina Navratilova interviews Novak DjokovicPhoto by Leonardo Fernandez/Getty Images

“We need to really chill because we are professionals and we want to play. We don’t want to quit.

“He’s played six hours in matches just grinding it out before, this was a view to the future for him. Protecting what the rest of the year holds.”

Given what she said about Coco Gauff after the French Open final, it’s expected that Aryna Sabalenka will have to deal with a hostile US Open atmosphere.

At least Djokovic, a good friend of hers, will be on hand to help her navigate the turmoil.