The TR Company

To ‘get the ball rolling’ means to get something started.

Examples:
Let’s get the ball rolling and learn some English idioms.
If you don’t get the ball rolling soon, you may not finish this project on time.

This idiom has a few variations. You can also say:
Set the ball rolling
Start the ball rolling

When we say, ‘the ball is in someone’s court’, it means it’s up to the person to make the next move. Sometimes, we may use the contracted form “the ball’s in your court” instead of saying “the ball is in your court”.

Examples:
I’ve given them all the information they need. The ball is in their court now and they need to come back to us with their ideas.
We’ve told you all you need to know about using English. Now the ball’s in your court.

If someone is ‘on the ball’, it means the person is very responsive and reacts very quickly in a situation.

Examples:
He’s really on the ball when it comes responding to emails.
My manager expects the team to be on the ball when we have to answer clients.

‘To keep your eye on the ball’ means to stay alert about something that is important to you especially if you are trying to reach a goal.

Example:
Keep your eye on the ball or else you may lose sight of your goal.
The opposite would be ‘to take your eye off the ball’ which means to lose focus and lose sight of your goal.

Example:
The swimming team started performing badly after the members took their eye off the ball.