Force diagrams demonstrate the forces acting on an object. For baseball there is always a force acting on the bat. Even when someone is holding the bat or the bat is on the ground their are still forces acting on it. If the bat is being held by the batter the forces acting on it would be the person holding the bat up against gravity and gravity pulling down on the bat. When a baseball is in the air the forces acting on it would be the lift the drag and gravity as shown in the picture below.