Bad new cocaine found in police bust (6)
I believe the answer is:
rancid
'bad' is the definition.
(I've seen this before)
'new cocaine found in police bust' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'cocaine' becomes 'C' (drugs abbreviation).
'found in' means one lot of letters goes inside another.
'police bust' becomes 'raid' (I've seen this in another clue).
'n'+'c'='nc'
'nc' put within 'raid' is 'RANCID'.
(Other definitions for rancid that I've seen before include "Turned -- malodorous" , "(Of fat/oil) stale and foul smelling" , "Like stale fat or oil" , "No longer fresh" , "Smelling or tasting of stale fat" .)