Cover for American gangster (4)
I believe the answer is:
hood
This clue is a double definition.
'cover' is the first definition.
(I know that hood is a more specific form of the action cover)
'american gangster' is the second definition.
(I've seen this before)
'for' acts as a link.
(Other definitions for hood that I've seen before include "this could provide cover" , "A cover; Bismarck sank it, 1941" , "Protective cover - violent criminal (slang)" , "Part of subfusc" , "Head covering of an American gangster" .)