The interesting thing about baseball pitching is that it's become such a science as to how a person is able to create a curveball versus a fastball. Subtle changes in how a baseball is held during the pitch will cause it to have a different type of trajectory during its delivery. For example, a curveball where the pitcher throws completely over handed with a vertical arm slot means that the ball will break straight downward when hurled toward the plate. Conversely, a curveball that is thrown when the arm slot is at an angle will cause the curve of the trajectory to be rather wide laterally.