Police-jacket letters (4)
I believe the answer is:
swat
'police-jacket letters' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for swat that I've seen before include "District of Pakistan; sharp blow" , ".`Twas quite a blow" , "Hit smartly" , "deliver blow" , "Twas something of a blow" .)