Support restraint on behalf of church (9)
I believe the answer is:
reinforce
'support' is the definition.
(I've seen this before)
'restraint on behalf of church' is the wordplay.
'restraint' becomes 'rein' (I've seen this before).
'on behalf of' becomes 'for' (I've seen this before).
'church' becomes 'ce' (abbreviation for Church of England).
'rein'+'for'+'ce'='REINFORCE'
(Other definitions for reinforce that I've seen before include "Strengthen or support with confrerie" , "increase support" , "give added support" , "Give added strength to" , "provide support" .)