... -hum, second half of game (4)
I believe the answer is:
pong
'hum second' is the definition.
'pong' can be an answer for 'hum' (I've seen this before). I am unsure of the 'second' bit.
'half of game' is the wordplay.
'half of' means to take half the letters.
'game' becomes 'pingpong' (ping-pong is a kind of game).
'pingpong' halved is 'PONG'.
Can you help me to learn more?
(Other definitions for pong that I've seen before include "In slang, a real stink" , "Stench" , "Smell unpleasantly" , "Reek" , "Horrid smell (informal)" .)