Sailor in fact a rating (3)
I believe the answer is:
tar
'sailor' is the definition.
(slang term for a sailor)
'in fact a rating' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TAR' is hidden within 'fact a rating'.
(Other definitions for tar that I've seen before include "Dark flammable liquid" , "Product of smoking cigarettes" , "Jack < to blacken" , "Black viscid substance" , "Black substance, used on roads" .)