Turn traitor? What's wrong with you? (6)

I believe the answer is:

defect

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'turn traitor?' is the definition.
(thesaurus)

I can't explain the rest of the clue.

(Other definitions for defect that I've seen before include "'Flaw, imperfection (6)'" , "Lack" , "Flaw - change sides" , "Shortcoming" , "To change sides dishonourably" .)

I've seen this clue in the Evening Standard.

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