Military personnel get poor backing in backstreet (6)
I believe the answer is:
troops
'military personnel' is the definition.
(synonyms)
'poor backing in backstreet' is the wordplay.
'backing' says the letters should be written backwards.
'in' indicates putting letters inside.
'backstreet' becomes 'ts' ('st' backwards).
'poor' back-to-front is 'roop'.
'roop' placed inside 'ts' is 'TROOPS'.
'get' acts as a link.
(Other definitions for troops that I've seen before include "Groups of soldiers" , "Military divisions" , "Bodies of soldiers" , "men" , "Cavalry" .)