Sponsor priest on trail going west (9)
I believe the answer is:
godfather
'sponsor' is the definition.
(I know that godfather is a type of sponsor)
'priest on trail going west' is the wordplay.
'priest' becomes 'father' (father is the title for a priest).
'on' means one lot of letters go next to another.
'trail' becomes 'dog' (synonyms).
'going west' is a reversal indicator (letters heading to the west or left).
'dog' backwards is 'god'.
'father' after 'god' is 'GODFATHER'.
(Other definitions for godfather that I've seen before include "gang boss" , "Baptismal sponsor" , "Religious relation, like Marlon Brando in movie" , "Mafia head" , "Mafia boss" .)