Mental strength tennis drill - Pass Me if You Can

When attacked, players tend to pay too much attention to the approaching player instead of the ball. 
If your opponent comes up to the net (on a short ball, serve and volleying etc.) make sure that you keep 
your eyes on the ball; your peripheral vision allows to keep track of where on the court your opponent is. 
 
So this tennis drill will emphasize staying calm and watching the ball as you are being pressured by the approaching player.

Drill:

Two players (A and B) are standing at the baseline on opposite sides. 
Player A has 3 balls ready to feed; he is the offensive player. B is the defending player for this drill. 
A puts the first ball in play with a "drop and hit" and moves up to the net. B stays at the baseline, defending. 
They rally the ball with A hitting every ball back to B. Player B will try to pass A with every single shot. 
If at any point the two players make an error, A will put the next ball in play with a gentle feed (still being at the net). 
After they play all 3 balls, player A moves back to the baseline and the two players start the drill over again. 
No points are being awarded for winning; just practice.
Play like this for about 10 minutes then switch roles: player B can be the offensive player and A works on passing shots.

Note: Quick decision making and shot selection is required by the defending player.