Sonic’s very new at Tennis so he probably doesn’t know how to play too well yet. Either way it doesn’t matter because even if he had been playing for 40 years it wouldn’t matter. Ryoma’s too good. Even if Sonic could give him a fight Ryoma could use the Selfless State. Ryoma wins.

Update 8 7 2020 Ryoma won’t be able to keep up with his speed. Sonic wins.