In Napoli, certainly, a force (6)

I believe the answer is:

police

'force' is the definition.
(police is a kind of force)

'in napoli certainly a' is the wordplay.
'in' indicates the answer is hidden within the clue.
'POLICE' is hidden in the letters of 'napoli certainly a'.

(Other definitions for police that I've seen before include "Law enforcers" , "Boys in blue" , "Nick" , "Keep watch on" , "Emergency service" .)

I've seen this clue in the Evening Standard.

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