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.
(..) Phones are down. Somebody go down and grab tech-ops... Hey... write down what you remember, people. There's gotta be some kind of a "blackout plan", right? Some kind of backup? There's an emergency resides? at the power plant. If he got the transmission lines, they never gonna get this back up. (..)2014 The Amazing Spider-Man 2