just an idea, do you think there should be a stat under XPs for mental strength or something similar? i know its a game but in professional tennis this plays such a huge part in matches. i just thought maybe when matches get tight, or if a player makes too many errors on the bounce, this stat could have a similar effect to low stamina (slow players down, make it more difficult to hit risk shots etc.).
obviously it would also work in the opposite way too. if players hit aces or great winners, they would become looser and easier to control.