They oppose any works by detective writer (9)

I believe the answer is:

naysayers

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'they oppose' is the definition.
The definition suggests an adverb but the answer is not.

'any works by detective writer' is the wordplay.
'works' is an anagram indicator (letters worked into a new form).
'by' is a charade indicator (letters next to each other).
'detective writer' becomes 'sayers' (I've seen this before).
'any' is an anagram of 'nay'.
'nay'+'sayers'='NAYSAYERS'

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I've seen this clue in The Times.

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