She never asked for backup, and no one heard from her again.

Behind her she could hear someone get on a radio and call for backup.

When it looked good, he should have called for backup.

"Two of these and you'll have to call for backup to get me back."

The two returned fire, took cover and called for backup.

Then he got into the front seat and called for backup.

In such cases, system images can be used for backup.

If asked, I would have chosen different people for backup.

After being fired on, the special forces moved back and called for backup.

They couldn't hear them call for backup, but it was moments away.