Take cover when one is after a gangster (6)

I believe the answer is:

capone

I'm a little stuck... Click here to teach me more about this clue!

'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 Globe and Mail and The Guardian.

Want a hint initially instead of a full solution? Install my app