Spoil function supported by clique (6)
I believe the answer is:
cosset
'spoil' is the definition.
(I know that spoil can be written as cosset)
'function supported by clique' is the wordplay.
'function' becomes 'cos' (mathematical function).
'supported by' means one lot of letters go next to another (in a down clue, some letters hold up others).
'clique' becomes 'set' (a clique is a social set).
'cos'+'set'='COSSET'
(Other definitions for cosset that I've seen before include "Care for overindulgently" , "pet" , "Pamper and spoil" , "Feather-bed" , "Treat with excessive indulgence" .)