The policeman called for 'backup' [=called for other police to come and help him] because the suspect was carrying a gun.
There was a traffic 'backup' [=('Brit') 'tailback'] for miles on the road because of the accident.
His role on the team is to be a 'backup' to the regular quarterback.
(..) You've got like five of them. Alright, here's what I'm gonna do. I'm gonna spot. Ready? What'd you see? - Too fast, nothing. Here we go. Three guys, one girl, all armed. God, I'd kill for some armor right now. - You're right, we need backup. - Yeah, much. You know what? Is that? - Yep. Are those? (..)2013 Iron Man 3