Английский словарь американских идиом - back up

{v.} 1. To move backwards. * /The train was backing up./ 2. To help or be ready to help; stay behind to help; agree with and speak in support of. * /Jim has joined the Boy Scouts and his father is backing him up./ * /The principal backs up the faculty./ * /Jim told us what had happened and Bob backed him up./ Compare: BACK OF(3), STAND BY(4). 3. To move behind (another fielder) in order to catch the ball if he misses it. * /The shortstop backed up the second baseman on the throw./