“Often takes were performed without the ball, which was later added in using VFX, but Chalamet was “adamant about it, for his own pride that he was going to play every point” with the actual ball, Safdie said. Even so, the director added, Chalamet and Kawaguchi, a player in real life, became so proficient at the choreography that when they weren’t using an actual ball, they visualized it so precisely they could improvise picking one up off the floor.
“It was so realistic that I thought there was a ball there,” Safdie said, noting that he couldn’t quantify how many shots involve a real ball and how many are effects.”
New York Times