Blockhead, to cheat officer! (4)
I believe the answer is:
dolt
'blockhead' is the definition.
(thesaurus)
'cheat officer' is the wordplay.
'cheat' becomes 'do'.
'officer' becomes 'lt' (I've seen this in other clues).
'do'+'lt'='DOLT'
'to' is the link.
(Other definitions for dolt that I've seen before include "Dimwit" , "Dullard" , "Dunce" , "Dull or stupid fellow" , "Halfwit" .)