Doctor was not nice -- a scientist (5,6)
I believe the answer is:
isaac newton
'scientist' is the definition.
(Isaac Newton is an example)
'doctor was not nice a' is the wordplay.
'doctor' is an anagram indicator.
'was'+'not'+'nice'+'a'='wasnotnicea'
'wasnotnicea' anagrammed gives 'ISAAC NEWTON'.
(Other definitions for isaac newton that I've seen before include "Laws of Motion man" , "Scientist who proposed the basic laws of motion" , "Seventeenth to eighteenth century English physicist/mathematician" , "English mathematician and physicist" , "he described it mathematically" .)