"backing him up" is a correct and usable phrase in written English.
It means to support or defend someone. Example: "I will be backing him up in the meeting tomorrow, as he presents his proposal."
"The White House is backing him up," Mr. Levin said.
"Right now Jeremy Lin is our starting point guard, and Baron is backing him up," Woodson said.
A five-piece band will be backing him up during the current tour.
He just needs his players to continue backing him up with their best shots.
A five-piece band will be backing him up on the current tour.
Meanwhile, Richter is enjoying a renaissance with Blackburn backing him up, which Sather argues is not coincidental.
Those eruptions were sometimes contrived, but they worked, because the player felt Parcells was backing him up in public.
Benny Trossi was going with the Yankees, and backing him up was $100 and a case of beer.
There was a very important man backing him up, but we do not know who it is".
It is just such a routine, with Mac in front and others backing him up, that Cumming and Barton were rehearsing.
Nixon lectures Agnew, backing him up against a coconut tree, until Agnew is bonked on the head by a falling coconut.
