First score in bag turns game (6)
I believe the answer is:
tennis
'game' is the definition.
(tennis is a kind of game)
'first score in bag turns' is the wordplay.
'first' says to take the initial letters.
'bag' becomes 'net' (I've seen this in other clues**).
'turns' says the letters should be written in reverse.
The initial letter of 'score' is 's'.
's'+'in'+'net'='sinnet'
'sinnet' in reverse letter order is 'TENNIS'.
(Other definitions for tennis that I've seen before include "Game (where love is nought?)" , "Racket sport" , "Game played on court" , "Racket-and-ball game" , "Table -, - elbow" .)