Often, when a projectile is thrown, techniques are used to cause the projectile to spin. For example, bowlers in cricket often deliberately apply spin to the ball. By causing the ball to spin, bowlers can make the ball follow a curved flight path, which makes it difficult for the opposing batter to read the ball's direction and hit it accurately.
The Magnus effect occurs when a spinning object is moving through air or water. To understand this, let's look at a spinning cricket ball. In cricket, as the spinning ball moves through the air, its spinning motion causes the air pressure on one side of the ball to be less than on the other side. Velocity increases (and air pressure decreases) on the side of the ball that is travelling in the same direction as the air around it. Velocity decreases (and air pressure increases) on the other side of the ball where the spin is moving against the direction of the air flow around it. The effects of the different velocity and air pressure on each side of the spinning ball cause it to curve towards the side with the higher velocity and lower air pressure.
Bowlers control the direction of the ball's curved trajectory by varying the ball's velocity, its axis of rotation and the direction in which it spins.