On reflection, it's wrong to trap game (6)
I believe the answer is:
tennis
'game' is the definition.
(tennis is a kind of game)
'on reflection it's wrong to trap' is the wordplay.
'on reflection' shows that the letters should be reversed in order.
'it's wrong' becomes 'sin' (wrong can mean a sin or crime).
'to trap' becomes 'net' (net is a type of trap).
'sin'+'net'='sinnet'
'sinnet' back-to-front is 'TENNIS'.
(Other definitions for tennis that I've seen before include "Game (where love is nought?)" , "Racket-and-ball game" , "Game of the Williams sisters and of Roger Federer" , "- elbow; - shoe" , "Popular racket game - anyone for it?" .)