See: BACK OF.
{prep.} 1. In or at the rear of; to the back of; behind. * /The garage is hack of the house./ * /Our car was in hack 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./