Top figure for gangster (6)
I believe the answer is:
capone
'gangster' is the definition.
(Al Capone)
'top figure' is the wordplay.
'top' becomes 'cap' (cap is a kind of top).
'figure' becomes 'one' (I've seen this before).
'cap'+'one'='CAPONE'
'for' is the link.
(Other definitions for capone that I've seen before include "US gangster (St Valentine's Day massacre)" , "Al - , notorious gangster" , "Italian-American gangster, d. 1947" , "Notorious criminal" , "Al ..., US gangster" .)