Colin acted badly in western (10)
I believe the answer is:
occidental
'western' is the definition.
('occidental' can be similar in meaning to 'western')
'colin acted badly' is the wordplay.
'badly' indicates an anagram.
'colin'+'acted'='colinacted'
'colinacted' is an anagram of 'OCCIDENTAL'.
'in' acts as a link.
(Other definitions for occidental that I've seen before include "Western" , "Westerner" , "Relating to the West" .)