Doctor gets round ban (4)
I believe the answer is:
veto
'ban' is the definition.
(veto can mean a ban or prohibition on something)
'doctor gets round' is the wordplay.
'doctor' becomes 'vet' (vet is a kind of doctor).
'gets round' becomes 'o' (I've seen this in other clues).
'vet'+'o'='VETO'
(Other definitions for veto that I've seen before include "A confused vote, altogether negative" , "Blocking vote" , "Authoritative prohibition" , "The right to forbid an action" , "Refusal to assent" .)