Punish crook (4)
I believe the answer is:
cane
I believe this clue is a double definition.
'punish' is the first definition.
(hit with cane)
'crook' is the second definition.
(I've seen this in another clue)
(Other definitions for cane that I've seen before include "Walking stick; punish" , "e.g. Bamboo stem" , "Stick; thrash" , "Slender stem of bamboo etc" , "Beat; sugar producer" .)