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.
(..) It's Erika. My God. The stalker! Never mind. It's open. Hitting her with a frying pan is a good idea. But we want a backup plan, just in case she isn't a cartoon! Let's get out of here! The one time they're not home! We'll leave. When we pass her... (..)1996 TvShow: Friends Title: The One After the Superbowl: Part 1 Season: 2 Episode 12