Incite maniac to leave Saint Immaculate (9)
I believe the answer is:
stimulate
'incite' is the definition.
(I know that incite is a more specific form of the action stimulate)
'maniac to leave saint immaculate' is the wordplay.
'to leave' suggests deleting specific letters.
'saint'+'immaculate'='saintimmaculate'
'saintimmaculate' with 'maniac' taken away is 'STIMULATE'.
(Other definitions for stimulate that I've seen before include "Animate, excite" , "Inspire enthusiasm" , "fire" , "Kindle?" , "Excite the feelings of" .)