The Warriors had just closed out the Memphis Grizzlies in the 2015 Western Conference semifinals, and Steve Kerr was looking especially sanguine. He’d popped out of the locker room, wearing a smile as loose as his plain sweats. He bounded to some postgame catering.



“The Western Conference finals,” he exclaimed, adding with a fan’s enthusiasm. “This is big stuff!”



The moment of innocent revelry was short-lived. The coach seized control of his body again. Above a baked bean tray, Kerr started pantomiming And1 mixtape handles, muttering to himself, “Now if we could just stop doing this … shit.”



Kerr’s stylistic preference was no secret. During the Game 6 blowout, from the FedEx Forum seats, you could hear the coach repeatedly hollering, “Move the ball!” or “Move the fucking ball!”



That was a different Warriors team, with habits less ingrained. They lacked the...