It's not good to make money on a game (9)
I believe the answer is:
badminton
'a game' is the definition.
(badminton is a kind of game)
'it's not good to make money on' is the wordplay.
'it's not good' becomes 'bad' ('bad' is the opposite to 'good').
'to make money' becomes 'mint'.
'bad'+'mint'+'on'='BADMINTON'
(Other definitions for badminton that I've seen before include "Court game" , "Racket sport" , "Racquet sport" , "in which rackets are involved" , "One sport" .)