Support nothing prior to Sarah's offer (8)
I believe the answer is:
proposal
'offer' is the definition.
(I know that proposal is a type of offer)
'support nothing prior to sarah's' is the wordplay.
'support' becomes 'prop' (prop up can mean to support).
'nothing' becomes 'O' (O resembles 0).
'prior to' is a charade indicator (letters next to each other).
'sarah' becomes 'Sal' (Sally is a common pet form of Sarah).
'prop'+'o'+'sal'='PROPOSAL'
(Other definitions for proposal that I've seen before include "Offer, of marriage say" , "put before the union?" , "Kind of offer, perhaps of marriage" , "a match might be arranged?" , "Offer - suggestion" .)