Sets posse off (5)
I believe the answer is:
poses
'sets' is the definition.
(posing is a kind of setting)
'posse off' is the wordplay.
'off' is an anagram indicator.
'posse' is an anagram of 'POSES'.
(Other definitions for poses that I've seen before include "Strikes attitude or sits for painter" , "Strikes attitude, maybe for photo" , "Sits (for artists)" , "Strikes attidude for artist" , "Sits for artist" .)