Backing in Jerusalem is guaranteed (4)
I believe the answer is:
sure
'guaranteed' is the definition.
(I've seen this in other clues)
'backing in jerusalem is' is the wordplay.
'backing' shows that the letters should be reversed in order.
'in' indicates the answer is hidden within the clue.
'erus' is hidden within 'jerusalem is'.
'erus' written backwards gives 'SURE'.
(Other definitions for sure that I've seen before include "See 12" , "Completely certain" , "Undoubtedly true" , "Confident sort of ruse" , "Certain, confident" .)