back of

[back of] or [in back of] {prep.} 1. In or at the rear of; to the back of; behind.

The garage is back of the house.

Our car was in back of theirs at the traffic light.

2. {informal} Being a cause or reason for; causing.

Hard work was back of his success.

The principal tried to find out what was back of the trouble on the bus.

3. {informal} In support or encouragement of; helping

Clones will be elected because many powerful men are back of him.

Get in back of your team by cheering them at the game.