Crane, US lawman, against it? (5)
I believe the answer is:
davit
'crane' is the definition.
(I know that davit is a type of crane)
'us lawman against it?' is the wordplay.
'us lawman' becomes 'da' (district attorney).
'against' becomes 'v' (abbreviation for 'versus').
'da'+'v'+'it'='DAVIT'
(Other definitions for davit that I've seen before include "nautical equipment" , "Lifeboat crane" , "device for lowering boat" , "Crane-like device for suspending or lowering ship's boats" .)