Game over for hawk (4)
I believe the answer is:
flog
'for hawk' is the definition.
(both can mean to sell)
'game over' is the wordplay.
'game' becomes 'golf game' (golf is a game).
'over' shows that the letters should be reversed in order.
'golf' backwards is 'FLOG'.
(Other definitions for flog that I've seen before include "- - a dead horse" , "Exchange for money" , "Scourge, whip" , "Beat with a whip or rod" , "Lash" .)