Clubs, later, reformed syndicate (6)
I believe the answer is:
cartel
'syndicate' is the definition.
(cartel is a kind of syndicate)
'clubs later reformed' is the wordplay.
'clubs' becomes 'c' (abbreviation used in card games such as bridge**).
'reformed' indicates anagramming the letters.
'later' with letters rearranged gives 'artel'.
'c'+'artel'='CARTEL'
(Other definitions for cartel that I've seen before include "Business syndicate in claret" , "Manufacturer's association restricting competition" , "Price-fixing association" , "Business combine in claret" , "Group of firms that agree fixed prices in order to limit competition" .)