Take cover when one is after a gangster (6)

I believe the answer is:

capone

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'gangster' is the definition.
(Al Capone)

'take cover when one is after a' is the wordplay.
'take cover when' becomes 'cap' (I can't justify this - if you can you should believe this answer much more).
'one is after' says to put letters next to each other.
'a' becomes 'one'.
'cap'+'one'='CAPONE'

Can you help me to learn more?

(Other definitions for capone that I've seen before include "Chicago gangster, d. 1947" , "Al ..., US gangster" , "Italian-American gangster, d. 1947" , "Notorious criminal" , "Hood" .)

I've seen this clue in The Guardian and The Globe and Mail.

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