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.
(..) Hey, mice, pass me a buffalo wing! No, to your left. Your left! - Tonight on "Knights"... - Now here's a good show! We got a white bronco heading east into the forest. Requesting backup. It's time to teach these madcap mammals their "devil may mare" attitudes just won't fly. Why you grabbing me? (..)2004 Shrek 2