Meaning: the initiative for taking action lies with somebody. To initiate an action now lies with the party that has the ball in their court.

Example Sentences:
1.- The entire family has stood by his decision to move to another country but the ball is in his court if he decides to change his mind at the last minute.
2.- I have already agreed to meet this guy to hear his proposal out but he did not show up in time, the ball is still in his court.

Meaning: very nervous person.

Example:
Before the interview, he was a bundle of nerves.

Meaning: (with) all one’s belongings.

Example:
Tired of their tantrums, the landlady asked her tenants to vacate the house, bag and baggage, in a week’s times.

Meaning: take a less important position.

Example: The founder of the company decided to take a back seat and let the board members run the business.