Stop protecting Capone – it's very common (9)
I believe the answer is:
prevalent
'common' is the definition.
(prevalent can mean common or widespread)
'stop protecting capone' is the wordplay.
'stop' becomes 'prevent' (stop can mean to prevent something).
'protecting' is an insertion indicator (inserted letters are held or protected).
'capone' becomes 'Al' (gangster Al Capone).
'prevent' placed around 'al' is 'PREVALENT'.
'aeur it's very' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for prevalent that I've seen before include "Commonplace" , "Widely accepted" , "Widespread - current" , "powerful" , "general" .)