Coach terrible cheat (5)
I believe the answer is:
teach
'coach' is the definition.
(I've seen this before)
'terrible cheat' is the wordplay.
'terrible' indicates an anagram.
'cheat' with letters rearranged gives 'TEACH'.
(Other definitions for teach that I've seen before include "Cheat (anag)" , "Pass on knowledge" , "Blackbeard" , "Work in school" , "Instruct, enlighten" .)