Really bad seeds spoilt red olives (9)
I believe the answer is:
'really bad seeds' is the definition.
(a bad seed is a bad person)
'spoilt red olives' is the wordplay.
'spoilt' indicates an anagram.
'redolives' anagrammed gives 'EVILDOERS'.
(Another definition for evildoers that I've seen is "People acting wickedly".)