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.
(..) We got vehicles from the Citadel. They're firing flares. They want reinforcements from Gas Town and the Bullet Farm. What is this?? Backup? Decoy?? It's a detour. Eyes right! Buzzards!!! Buzzards right!! Eyes on! Eyes on!! Should we turn around and run 'em into our backup? No! We're good. We fang it!! Thunder up! Here we go!! Prepare the shooter! Morsov! (..)2015 Mad Max: Fury Road