Stop protecting Capone - it's very common (9)
I believe the answer is:
prevalent
'very common' is the definition.
'prevalent' can be an answer for 'common' (prevalent can mean common or widespread). I am not certain of the 'very' bit.
'stop protecting capone' is the wordplay.
'stop' becomes 'prevent' (to prevent something is to stop it).
'protecting' means one lot of letters goes inside another (inserted letters are held or protected).
'capone' becomes 'Al' (gangster Al Capone).
'prevent' enclosing 'al' is 'PREVALENT'.
'it's' is the link.
Can you help me to learn more?
(Other definitions for prevalent that I've seen before include "Common" , "Ruling" , "Commonplace" , "Widely accepted" , "powerful" .)