I have a kind of "complex" suggestion. I'll try to explain to the best of my english abilities. Sorry for any mispelling.
So, it has to do with reachable/unreachable balls. When the opponent strikes the ball, i think (correct me if i'm wrong) the game is able to "calculate", based on the ball struck and the actual time the human player started to go for it (along with the chosen player speed and other variables, such as surface), if that ball is going to be:
1) reachable and returnable;
2) reachable, but with need to do a stretch or slide movement at full speed;
3) reachable, but unreturnable (net, long, wide, ball that lands on your own court);
4) a winner from the opponent, by a close margin;
5) a winner with no chance of getting near the ball.
Depending on that result, the game can trigger different animations, such as sliding, streching and grindind for cases (2), (3) and (4) or standing still or giving up on the run in the middle of it on (5).
If the player reacts on time, (1, 2, 3 or 4) but fails to keep runing at full speed in the correct direction or just gives up, animation (5) would be triggered.
I thought of this because that's kinda what happens on court. When you have doubts about being able to reach the ball or not, you could go full on towards it or just give up.
Hope i could make myself clear and help you solve this important puzzle.