Basically:

Kawhi got hurt.

Spurs diagnosed him with a chronic, degenerative quadriceps injury. Kawhi was coming up on the end of his contract and wanted the max, but the Spurs were apparently hesitating after diagnosing him.

Kawhi shopped around through various specialists, almost all agreed with the Spurs initial diagnosis.

Kawhi found a doctor in New York that told him what he wanted to hear, that it was a normal injury that could be fixed, and Kawhi began aggressively rehabbing with them.

During this time, Kawhi didn’t communicate with the team. Pretty much the entire year, reports said he was 2-4 weeks away from returning. And every 2-4 weeks, a new report would come out saying it would be 2-4 more weeks.

While there, he sequestered himself with his Uncle, Dennis. Dennis was like a father figure to Kawhi after his own father had been murdered. Dennis was also Kawhi’s agent, and seemed like he wanted to start his own agency like Rich Paul did with LeBron. He also asked the Spurs to give him a job in the Spurs FO, which they declined. It is widely believed that Dennis was in Kawhi’s ear at this time and essentially convinced him that he was too big a star to be constrained to a small market like San Antonio.

Apparently, Spurs reps went to see him in New York to check on him, and he hid from them and refused to talk to them. He was never on the bench in street clothes, even during the Playoffs. His teammates became frustrated with constantly being asked when he’d return, and a few even said some sharp things about the situation.

Less than a week after the Spurs were eliminated from the Playoffs, Kawhi, who had basically not made a public appearance in months, was seen at an LA Dodgers game. Shortly thereafter, Kawhi demanded a trade and named Los Angeles as his preferred destination.

Kawhi was traded to Toronto for far below his value, won a championship with the Raptors, and then signed with the Clippers in free agency. To add insult to injury, the Clippers medical team stated that Kawhi had a chronic, degenerative quadriceps injury which the Spurs medical staff had initially diagnosed him with.

As a result of this, many Spurs fans feel that Kawhi essentially quit on the team and hid behind his injury as an excuse. Dennis also tried to throw the Spurs under the bus, claiming the medical staff was incompetent (which was proved wrong a few years later) and that Kawhi wanted a trade because the Spurs were pressuring him to come back before he was healed (which is odd considering the Spurs were the first team to adopt the practice of load management, including resting Kawhi himself in some back-to-back games pre-injury). Of course, the media ran with those claims and celebrated the downfall of the once “classy” Spurs organization, so it was a rough time to be a Spurs fan.