... ganger backing reputation up (7)
I believe the answer is:
foreman
'ganger' is the definition.
(thesaurus)
'backing reputation up' is the wordplay.
'backing' becomes 'for' (I've seen this in another clue).
'reputation' becomes 'name' (someone's good name is their reputation).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'name' written backwards gives 'eman'.
'for'+'eman'='FOREMAN'
(Other definitions for foreman that I've seen before include "Gaffer, overseer" , "Gaffer, boss" , "spokesman" , "Male supervisor" , "Fellow in charge" .)