A doctor stood up for him (7)
I believe the answer is:
ambrose
'him' is the definition.
'a doctor stood up' is the wordplay.
'doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus).
'stood up' becomes 'rose' (I've seen this in other clues).
'a'+'mb'+'rose'='AMBROSE'
'for' is the link.
(Other definitions for ambrose that I've seen before include "handle for him" , "name" , "Church Father" , "Bishop of Milan once" , "saint, maybe" .)