Start the ball rolling =start an activity and encourage others to join in.

• I decided to start the ball rolling and got up to dance.
• To start the ball rolling , the government was asked to contribute a million dollars to the fund.
• I would like you each to tell us why you have decided to do a creative writing course; Marie, would you start the ball rolling, please?

The ball is in your court = It is your responsibility now; it’s up to you.  You have to do something now before any progress can be made.

• I have helped him in every way I can; the ball is in his court now.
• The ball is in their court , so we will have to wait and see what they do.
• Well, they have invited you , so the ball is in your court now.  Do you want to go out with them or not?

On the ball = aware of, quick to understand and react to new ideas/methods.

• Maintaining contacts with customers keeps me on the ball.
• Don’t forget that our rival companies are on the ball and if we don’t act quickly and do something off our own bat , they will secure the contract for themselves.