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.
(..) BRUCE WAYNE RESCUES EMPLOYEE Sir. Get down. Sir, I said, get down, now! Can we get some backup here? Hey. Hey. Don't do it! HEY! Lois. Crime Lab, on . (..)2016 Batman v Superman: Dawn of Justice