Man, thief, heading off (4)
I believe the answer is:
rook
'man' is the definition.
(rook is a kind of man)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for rook that I've seen before include "Defraud; bird; chessman" , "Black bird - cheat - chess piece" , "A bird; overcharge" , "flier" , "Another name for castle in chess" .)