Sharp intelligence unit over to entrap investigators (6)
I believe the answer is:
acidic
'sharp' is the definition.
(I've seen this before)
'intelligence unit over to entrap investigators' is the wordplay.
'intelligence unit' becomes 'CIA' (Central Intelligence Agency).
'over' shows that the letters should be reversed in order.
'to entrap' is an insertion indicator.
'investigators' becomes 'cid' (I've seen this in other clues).
'cia' back-to-front is 'aic'.
'aic' placed around 'cid' is 'ACIDIC'.
(Other definitions for acidic that I've seen before include "scathing?" , "Sarcastic or sour" , "Containing a sour-tasting substance" , "Cutting" , "Unpleasant" .)