Adbono;
The tee is a classroom to refine the player's swing.
"High tee" to develop carry on the ball. "Low tee" to develop fast hands and strong fingers. Tee on the corner to hit to the opposite field. The player set his routine and phase of work. When you are in the game it is "pass or fail".
"Swinging hard" = pitcher's change up" and over swing.
Bob