Smell of game? Not half! (4)
I believe the answer is:
pong
'smell' is the definition.
(pong can informally mean a bad smell)
'game? not half' is the wordplay.
'game?' becomes 'pingpong' (ping-pong is a kind of game).
'not half' indicates taking half.
'pingpong' cut in half is 'PONG'.
'of' acts as a link.
(Other definitions for pong that I've seen before include "Bad smell" , "hum" , "Stench" , "Nasty smell (informal)" , "Horrid smell (informal)" .)