Police operation (5)
I believe the answer is:
sting
'police operation' is the definition.
(sting can mean a police operation)
This is all the clue.
(Other definitions for sting that I've seen before include "English musician, b. 1951 -- a sudden pain" , "Pole from Glasgow" , "The pain caused by bee or nettle" , "aka Gordon Sumner" , "con trick" .)