I was watching a game yesterday and at this level (I started playing tennis after I entered junior high school), it seems that the victory or defeat is almost determined by whether or not the serve can enter.
Since it was free time to support it, I tried to take the probability that the army would serve at the time of service.
After all, at this level, it was concluded that if the probability of serving would exceed the opponent, you could almost win.
So anyway persistently tell children to serve anyway
The data is still strong