Doctor cites case of agoraphobic recluse (7)
I believe the answer is:
ascetic
'recluse' is the definition.
(I've seen this in another clue)
'doctor cites case of agoraphobic' is the wordplay.
'doctor' indicates anagramming the letters.
'case of' means to remove the middle letters (like emptying a case).
'agoraphobic' with its centre removed is 'ac'.
'cites'+'ac'='citesac'
'citesac' with letters rearranged gives 'ASCETIC'.
(Other definitions for ascetic that I've seen before include "Self-disciplined person" , "One practices self-denial as a spiritual discipline" , "One who practises extreme self-discipline" , "Self-denying, Spartan" , "Austere, Spartan" .)