Bad guy (4)
'bad guy' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for enemy that I've seen before include "Yemen (anag.)" , "Armed adversary" , "Antagonist" , "Time" , "Foe, adversary" .)
(Other definitions for heel that I've seen before include "Lean over; part of foot" , "instruction to setter, say" , "despicable person" , "one regarded with contempt" , "Contemptible person" .)