Single-handedly capturing top criminal (2,6)
I believe the answer is:
al capone
'criminal' is the definition.
(I've seen this before)
'single-handedly capturing top' is the wordplay.
'single-handedly' becomes 'alone' (I've seen this in another clue).
'capturing' means one lot of letters goes inside another.
'top' becomes 'cap' (both can mean to beat or outdo).
'alone' placed around 'cap' is 'AL CAPONE'.
(Other definitions for al capone that I've seen before include "Famous gangster" , "US gangster in Chicago, arrested for tax evasion" , "Chicago gangster known as Scarface" , "Hood" , "Notorious Chicago gangster nicknamed Scarface" .)