Doctor bears out subversive (8)
I believe the answer is:
saboteur
'subversive' is the definition.
(thesaurus)
'doctor bears out' is the wordplay.
'doctor' indicates anagramming the letters.
'bears'+'out'='bearsout'
'bearsout' anagrammed gives 'SABOTEUR'.
(Other definitions for saboteur that I've seen before include "Deliberate destroyer" , "Our beats (anag) - fifth columnist" , "Vandal" , "Deliberate wrecker" , "Underminer, wrecker" .)