Magnus Force
The Magnus force (or sometimes called the Magnus Effect) is a force on a rotating cylinder in a fluid flowing perpendicular to the axis of the cylinder, the force is perpendicular to both the flow direction and cylinder axis. In the case of a baseball, the baseball in the air will create a sort of whirlpool around the rotating air. On one side the whirlpool would be working in the same direction as the drag force, causing the velocity to increase. While on the other side the drag force will be working against the direction causing the velocity to decrease. See Diagram.
