A bad can is thrown in free (6)
I believe the answer is:
rancid
'a bad' is the definition.
(thesaurus)
'can is thrown in free' is the wordplay.
'is thrown' is an anagram indicator (I've seen 'was thrown' mean this).
'in' is an insertion indicator.
'free' becomes 'rid' ('rid' can be a synonym of 'free'**).
'can' with letters rearranged gives 'anc'.
'anc' inserted inside 'rid' is 'RANCID'.
(Other definitions for rancid that I've seen before include "Rotten; high" , "Stinking" , "Noxious" , "(Of fatty foods) stale" , "(Of butter) stale" .)