Objective setter's role -- I fail regularly (9)
I believe the answer is:
impartial
'objective' is the definition.
(I've seen this before)
'setter's role i fail regularly' is the wordplay.
'setter's' becomes 'im' (I've seen this in other clues**).
'role' becomes 'part' ('part' can be a synonym of 'role').
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'fail' are 'al'.
'im'+'part'+'i'+'al'='IMPARTIAL'
(Other definitions for impartial that I've seen before include "Showing lack of favouritism" , "Unbiased" , "Disinterested" , "Objective" , "Treating all rivals equally" .)