Scowl seeing setter's in favour (7)
I believe the answer is:
grimace
'scowl' is the definition.
(thesaurus)
'setter's in favour' is the wordplay.
'setter's' becomes 'im' (I've seen this in other clues).
'in' is an insertion indicator.
'favour' becomes 'grace' ('grace' can be a synonym of 'favour').
'im' put inside 'grace' is 'GRIMACE'.
'seeing' is the link.
(Other definitions for grimace that I've seen before include "Nasty expression" , "Smirk" , "betray disgust" , "unpleasant expression" , "Disgusted expression" .)