Rank supervised detectives (6)
I believe the answer is:
rancid
'rank' is the definition.
(I've seen this before)
'supervised detectives' is the wordplay.
'supervised' becomes 'ran' (I've seen this in another clue).
'detectives' becomes 'CID' (abbreviation for Criminal Investigation Department).
'ran'+'cid'='RANCID'
(Other definitions for rancid that I've seen before include "Rank in smell and taste" , "Rank-smelling." , "Unpleasantly stale" , "Smelly and going bad" , "Tasting or smelling sour, butter say" .)