One theory for why Chauvin stepped on Floyd's throat for 8 minutes with his hands in his pocket is that he was training 2 rookies on site and he was afraid that

One theory for why Chauvin stepped on Floyd's throat for 8 minutes with his hands in his pocket is that he was training 2 rookies on site and he was afraid that backing down to pressure from the public (people yelling at him to stop) would make him look weak and lose face in front of the rookies. And the rookies were deferential to Chauvin's seniority. It's easy to imagine that if it was an overeager rookie on Floyd's neck, the rookie wouldn't have had his hands in his pocket and Chauvin would have told him to ease off a few minutes earlier before Floyd died. In a sense it's not too different from the mindset when a captain crashes a plane over the better judgement of a junior co-pilot.