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.
(..) M'kay? They got nothin' on us. Let's just be mellow, OK? What're you doing? No! What the fuck are you doing? This is Officer Mackenzie, I need backup. Assailants turning south down Lexington Avenue. I'm in pursuit. Oh, God damn it, Kyle! " Car chase city, (..)2006 Tenacious D in the Pick of Destiny