Watch: Djokovic Plays Catch With Zverev

Practice isn't confined to the court when Novak Djokovic and Alexander Zverev get together. The world No. 1 took time out from training on Arthur Ashe Stadium court to test Zverev's hands. More: Greatness Revisited, the Pete Sampras Story Watch the 17-time Grand Slam champion launch a few balls up into the stands where Zverev was waiting.