Rogue cowboy perhaps unfit (8)
I believe the answer is:
improper
'unfit' is the definition.
(I've seen this before)
'rogue cowboy' is the wordplay.
'rogue' becomes 'imp'.
'cowboy' becomes 'roper' (I've seen this in another clue).
'imp'+'roper'='IMPROPER'
'perhaps' is the link.
(Other definitions for improper that I've seen before include "Indecent or unsuitable" , "Naughty" , "Not fitting" , "Hardly meet" , "Not in line with accepted standards of morality" .)