Many sports such as baseball or playing with your dog inculde playing catch. Within playing catch comes a lot of physics. Understanding projectiles and freefall all in one. When one person throws the ball they throw it into the air so that it reaches its full height, comes back down, then the other person catches the ball before in reaches the ground. To understand this you will have to take into respect gravity. Gravity will affect the balls potential height and the velocity at which it will go at to reach the designated spot at which one is trying to hit. The higher you throw the ball the shorter distance it will go and the more force or velocity it will need. But the lower you throw it the farther it will go becuase of the less gravitational pull that is exerted on the ball.