Serves initially in net — a reversal for this game? (6)
I believe the answer is:
tennis
'this game?' is the definition.
(tennis is a kind of game)
'serves initially in net a reversal' is the wordplay.
'initially' indicates taking the first letters.
'a reversal' is a reversal indicator.
The first letter of 'serves' is 's'.
's'+'in'+'net'='sinnet'
'sinnet' reversed gives 'TENNIS'.
'for' is the link.
(Other definitions for tennis that I've seen before include "Game played with racket and ball" , "Game played on court" , "Racquet-game" , "Real or lawn game" , "Ball game with a net" .)