“He returned to the Saints to backup Drew Brees.”
Not to nitpick, but backup can be a noun (he was stuck being a backup) or an adjective (he was stuck being the backup quarterback) but never a verb.
He returned to back up Drew Brees.
If you see the phrase backup Drew Brees, the world has come to an end, because it means that Drew Brees has become a backup, and that’s just not reality.
I mean, I’m a Patriots fan, but come on. Brees as a backup?
(P.S. You can get your back up, but that’s totally different. You can also back up your hard drive — and you should — but the copy you make is a backup.)
(P.P.S. It’s never, ever hyphenated. There is no back-up in English.)