One of the simplest baseball drills that only requires one person, a glove, a ball and a wall exhibits one of the basic yet essential physics concepts: Newtons third law. Newton's third law states that if something applies a force on an object, that object will apply a force of equal magnitude in the opposite direction.
So when training for baseball, someone can throw a baseball against a wall with a certain force and the ball will come off the wall with the initial magnitude it first hit the wall with, but in the opposite direction. Newton's third law didn't take into account friction so the ball will be subjected to air resistance and won't make it back to the person with the same velocity but for the instances it strikes the wall and comes off the wall, air resistance is negligible. Therefore, Newton's third law can be observed.