The most common and most likely answer to this crossword clue is the 14 letter word REINFORCEMENTS
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result REINFORCEMENTS
Buddy explains!

The straight part
We know that "Backups" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case backups = reinforcements.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does REINFORCEMENTS mean?
REINFORCEMENTS noun- The act, process, or state of reinforcing or being reinforced.
- A thing that reinforces.
- (in the plural) Additional troops or materiel sent to support a military action.
- The process whereby a behavior with desirable consequences comes to be repeated.