Doctor was not bad (6)
I believe the answer is:
watson
'doctor' is the definition.
(Dr Watson from Sherlock Holmes stories)
'was not bad' is the wordplay.
'bad' is an anagram indicator.
'was'+'not'='wasnot'
'wasnot' with letters rearranged gives 'WATSON'.
(Other definitions for watson that I've seen before include "I helped detective" , "Sherlock Holmes's doctor buddy" , "Sherlock Holmes's doctor companion" , "Doctor colleague of Sherlock Holmes" , "Holmes' assistant" .)