Novak Djokovic was an angry man long before a shoulder injury and a break of service saw the US Open explode on Monday morning.
According to keen observers, the 33-year-old has been spotted throughout his 2020 US Open campaign for grand slam No. 18 more irate than normal.
The frustrated tournament favourite on Monday fell behind 5-6 in the first set of his fourth-round match against Spain's Pablo Carreno Busta when he hit a ball in the direction of a female official.
It struck her in the throat and she could be heard gasping.
Djokovic held up his hand in apology, then walked over to check she was OK and after a few minutes, she got up and walked off the court.
Following around 10 minutes of discussions with the tournament referee, the umpire declared that Carreno Busta had won by default.
A USTA spokesperson said the line judge was "doing OK" after receiving treatment from medical staff.
It emerged on Monday night that Djokovic had been using rage as a baffling tactic to keep his energy levels high in a tournament taking place behind closed doors with no fans in attendance in the middle of the coronavirus pandemic.
According to freelance tennis journalist Reem Abulleil, Djokovic has been uncharacteristically frustrated even as he cruised into the fourth round, dropping just one set to England's Kyle Edmund.
Riding the fine line between energy-boosting adrenaline and all-consuming, uncontrollable rage, Djokovic paid the price of his poor strategy when he flippantly flicked a forehand towards the back of the court — ending his tournament on the spot.
Djokovic has also had to deal with the prickly fall out to his dramatic move last week to establish the Professional Tennis Players Association.
The move to put heat on the ATP Tour was labelled "tone deaf" by Aussie tennis great Todd Woodbridge last week.
Abulleil told the No Challenges Remaining Podcast Djokovic's apparent strategy seemed out of place as he struggled with anger even as he eased past Damir Dzumhur and Jan-Lennard Struff in straight sets earlier in the tournament.
"Because there are no fans he has been so angry during matches, even when he's cruising," Abulleil said.
"Because that's how he's been getting the energy that he usually gets from the crowd. And he has been noticeably angry in various points in various matches.
"He's definitely been angry and I noticed that when I was thinking about how he's been doing that a lot because in an empty stadium he feels like he needs to do that. And maybe that contributed to the whole situation too. It was the first set. He'd lost one break. It wasn't that big of a deal."
His reaction was.
Nearly three hours after his indiscretion, Djokovic took to Instagram to apologise for his outburst.
"This whole situation has left me really sad and empty. I checked on the lines person and the tournament told me that thank God she is feeling OK," he wrote.
"I'm extremely sorry to have caused her such stress. So unintended. So wrong. I'm not disclosing her name to respect her privacy.
"As for the disqualification, I need to go back within and work on my disappointment and turn this all into a lesson for my growth and evolution as a player and human being. I apologise to the @usopen tournament and everyone associated for my behaviour.
"I'm very grateful to my team and family for being my rock support, and my fans for always being there with me. Thank you and I'm so sorry."
In his most recent post to Twitter, Djokovic asked fans to have sympathy for the linesperson.
"Dear #NoleFam thank you for your positive messages.. Please also remember the linesperson that was hit by the ball last night needs our community's support too. She's done nothing wrong at all. I ask you to stay especially supportive and caring to her during this time," he wrote.
"From these moments, we grow stronger and we rise above. Sharing love with everyone. Europe here I come."
US Open tournament referee Soeren Friemel was left the front the press instead, revealing why the decision was made to eject Djokovic.
"Defaulting a player at a Grand Slam is a very important, very tough decision and for that reason, and it doesn't matter if it's on Ashe, if it's No 1 or any other player on any other court, you need to get it right," he said.
"You need to make the right decision and everyone on court was aware of what was at stake and surely, that's always in the back of everyone's mind, but we need to leave that out and make sure that we base it on the facts and on the rules so that we get the right decision there.
"I don't think there was any chance of any opportunity of any other decision other than defaulting Novak, because the facts were so clear, so obvious, that the line umpire was clearly hurt and Novak was angry, he hit the ball recklessly, angrily back and taking everything into consideration, there was no discretion involved."
Tennis commentator David Law told The Tennis Podcast Djokovic showed he was not up to the demands of leadership by failing to front the press on his way out the door at Flushing Meadows.
"I know it's stressful. I know it's a grand slam, I know how devastated you are. But when you're the leader. When you're the former ATP Tour Council former president and you are now the head of the new Professional Tennis Players Association, you don't just run away," Law said.
"You don't leave it there and escape into the night with a statement left behind you.
I'm disappointed with that.
"When things go wrong for him like this, he can go. He just leaves."