Ecstasy among RC saints confused scriptwriter (9)
I believe the answer is:
scenarist
'scriptwriter' is the definition.
(I know that scriptwriter can be written as scenarist)
'ecstasy among rc saints confused' is the wordplay.
'ecstasy' becomes 'E' (informal term for the drug).
'among' means one lot of letters goes inside another.
'confused' indicates an anagram.
'rc'+'saints'='rcsaints'
'rcsaints' anagrammed gives 'scnarist'.
'e' placed within 'scnarist' is 'SCENARIST'.
(Other definitions for scenarist that I've seen before include "Deviser of drama" , "Author" .)