Beat heavily: game over (4)
I believe the answer is:
flog
'beat heavily' is the definition.
(flog can mean to beat or whip)
'game over' is the wordplay.
'game' becomes 'golf' (golf is an example).
'over' is a reversal indicator.
'golf' reversed gives 'FLOG'.
(Other definitions for flog that I've seen before include "Keep hitting" , "Hit - sell" , "Thrash" , "Whip severely" , "Exchange for money" .)