Unrest curtailed in city (3)
I believe the answer is:
rio
'city' is the definition.
(Rio is an example)
'unrest curtailed' is the wordplay.
'unrest' becomes 'riot' (I have seen 'Civil unrest' mean 'riot' so perhaps 'unrest' could also mean 'riot').
'curtailed' means to remove the last letter.
'riot' with its final letter taken away is 'RIO'.
'in' is the link.
(Other definitions for rio that I've seen before include "Erstwhile home of Biggs" , "Manchester United player in South American city, in short?" , "place of carnival" , "Brazilian city and port" , "Spanish word for river" .)