Against South American cleric returning (6)
I believe the answer is:
versus
'against' is the definition.
(as in one sports team versus another)
'south american cleric returning' is the wordplay.
'south' becomes 's' (abbreviation).
'american' becomes 'US' (United States).
'cleric' becomes 'Rev' (abbreviation for Reverend).
'returning' is a reversal indicator.
's'+'us'+'rev'='susrev'
'susrev' backwards is 'VERSUS'.
(Other definitions for versus that I've seen before include "In opposition to" , "Preposition meaning against, as in contest" , "playing" , "Opposed to" , "Set against" .)