Uncle, one prodding muscle of Spooner? (10)
I believe the answer is:
pawnbroker
'uncle' is the definition.
(informal term for a pawnbroker)
I don't understand how the remainder of the clue works.
(Other definitions for pawnbroker that I've seen before include "One who does business" , "One lending against deposited goods" , "Uncle's" , "Lender against items" , "His sign is three balls" .)