I just watched the whole replay of what happened in that match vs Careno-Busta. At 5-5 in the 1st set with the score 0-15, Djokovic slipped and landed on his left hand, wrenching his shoulder in the process. He called for a trainer and after the injury break, at 0-30 he went on to lose that game 15 --- umm 50 I guess....Never thought how they score the winning point when the score is at 40 lol. Anyways with the games at 5-6 for Careno-Busta, Djokovic obviosuly frustrated with how things were going, then hit a ball to his left and hit a female line judge in the neck. Djokovic was obviously in trouble in the match and might have had to retire anyways due to his left shoulder being injured. Careno-Busta was also playing very well before Djokovic slipped. Djokovic has had similar incidents in the past that were also unintentional but where he failed to control his emotions and placed others nearby in physical danger as a result of his actions. Djokovic for sure did not mean to hurt the line judge, however I have never seen a professional tennis player hit a ball with some force as Djokovic did, towards any line judge or ball boy/girl. Denis Shapovalov in frustration in his first year when I believe he was 17 yrs old, did hit the official judge seated in the chair beside the middle of the court in the eye. The official required surgery which Shapo offered to and did pay for. Shapo also lost that match by default. The rules are clear. It does not matter if there was intention or not. If you choose to allow your emotions to rule your actions, you are responsible. Four points before this incident, Djokovic hit another ball in anger into a side fence. Novak tried to argue his side in his defense but what is troubling is that it took 16 minutes before the Officials actually came to the final decision that Djokovic would suffer the Default/Loss as a result of his actions. This was a black and white matter. This should not have taken any longer than 2-3 minutes and 5 at the most. What is very strange is that the Officials could not, under the rules, review a video replay for this incident. That makes zero sense. The Officials were also wrong in stating that because the line judge had to be removed from the court and treated, that Novak had to lose by default. It in fact does not matter if anyone was actually hurt or not. The actions of the player, as per the rules, are what should make these decisions fairly easy to make. It does not matter how good that player is.
As good as Djokovic is as one of, and possibly the best players tennis has ever seen, he needs some anger management help.