A standard idiom deriving from Tennis. It means that the situation is now the responsibility of the Chinese.
See here: Ball is in your court - UsingEnglish.com
The ball is in the Chinese court=? Does it contain any slang or idiom? Thanks!The senior Chinese leadership should respond by expressing serious interest in talks at the presidential or prime ministerial level. In ancient days, the Olympics were a time to suspend conflict. In that spirit, the two sides should get to work to prepare for a visit by the Dalai Lama in November, followed by top-level negotiations aimed at a historic resolution of the Tibet question.
The ball is in the Chinese court
The Tibetan side (according to the writer) have made their demands, put their point of view, are willing to have talks, etc. So they have played the ball over to China's side. The ball is now on China's side of the net - it is now for China to decide how to make the next play.
Anglika & Raymott,
Thank you very much for your answers.