Forget the Australian Open, the French Open, Wimbledon or the US Open - a new craze of 'speed bowling' could be set to sweep the world of tennis.
Both Novak Djokovic and Maria Sharapova will be in action when the US Open begins in Monday, and they have been warming up in a fairly unorthodox fashion.
The aim of the game is to complete a strike using three tennis balls - and it was the Serbian who came out on top.
Watch the video below:
Germany
Switzerland
Hungary
Scotland
