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.
(..) before intercept. Once mark's engine shuts off... We'll know our intercept point and velocity. Vogel, you're Beck's backup. Everything goes well, you pull them on board with the tether. If anything goes wrong, you go out after him. Yep. (..)2015 The Martian