At the start of training camp, early last October, the Boston Celtics’ social-media team posted a video of Jaylen Brown, the team’s All-Star guard, practicing his dribble. In it, Brown, his back to the camera, pounds a few hard dribbles with his right hand, then shifts the ball to his left. The ball begins to stray.

Brown hitches it back. Then the ball swings farther to the left, and Brown pulls it back too sharply; he has to step forward to corral it. He regains control for a few dribbles, but, when the clip cuts off, the ball is about to bounce out of the frame.

The video disappeared from the Celtics’ channels, but not before it was widely shared, often with unflattering commentary. Just weeks earlier, Brown had signed a contract for about three hundred million dollars, the largest in N.B.

A. history. This was not a surprise; he was the first player to be eligible for so much money, partly on the basis of being named to a list of the league’s best players in the season prior.

And he is an aggressive, dynamic scorer, plus a tenacious defender capable of guarding anyone. Still, there was the matter of that dribble. The last time Brown had played in an N.

B.A. game, in the deciding contest of the Eastern Conference Finals, against the Miami Heat, he’d had eight turnovers, many of them mishaps while dribbling with his left hand.

The favored Celtics lost that game, and, with it, the series, to the underdog Heat, in a blowout. Never mind that the team’s best player, , h.