He wanted the game ball because of his record 64 point game. His equipment manager got the ball and brought it to the back. The Pacers equipment manager got a reserve ball and gave to the Pacers rookie because he scored his first points in a regular season game. Giannis didn't know his equipment manager already got the ball for him, thought the Pacers got the actual game ball, and he went berserk. I think at one point, he was chasing the Pacers equipment manager to their locker room haha. He went back on the court after storming the Pacers locker room and was demanding Haliburton to go get him the ball. But in the end, it was all a misunderstanding and everyone got what they wanted, I guess?