Harsh neighbourhood police officer must flee (6)
I believe the answer is:
strict
'harsh' is the definition.
(I've seen this before)
'neighbourhood police officer must flee' is the wordplay.
'neighbourhood' becomes 'district'.
'police officer' becomes 'di' (detective inspector).
'must flee' indicates named letters should be taken away.
'district' with 'di' taken away is 'STRICT'.
(Other definitions for strict that I've seen before include "Demanding obedience to rules" , "Rigid or stern" , "Severe, stern" , "Exacting, unsparing" , "Allowing no deviation from a standard" .)