Prohibition sees cop retiring (3)
I believe the answer is:
ban
'prohibition' is the definition.
(ban is a kind of prohibition)
'cop retiring' is the wordplay.
'cop' becomes 'nab' ('nab' can be a synonym of 'cop').
'retiring' says the letters should be written in reverse.
'nab' reversed gives 'BAN'.
'sees' acts as a link.
(Other definitions for ban that I've seen before include "Exile" , "Officially prohibit" , "Bar, prohibition" , "Hungarian governor < to forbid" , "Stop" .)