Game's up for hawk (4)
I believe the answer is:
flog
'hawk' is the definition.
(both can mean to sell)
'game's up' is the wordplay.
'game' becomes 'golf' (golf is an example).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'golf' backwards is 'FLOG'.
'for' acts as a link.
(Other definitions for flog that I've seen before include "Beat with whip or slangily sell" , "-- Hitler" , "- - a dead horse" , "Swing a cat, perhaps" , "Exchange for money" .)