A ball that is spinning is always easier to return than a ball that is not spinning because a ball that spins has stability at range. The frontiersmen of America had worked this out and used it with their rifles. If you look down the barrel of a rifle, you'll see it has what are called 'lands' down the barrel. These are grooves cut into the barrel that twist in one direction, causing the bullet to spin. This gives the projectile stability at range. Without the lands, the projectile would stray off course after about 50 meters and certainly by a hundred. For history buffs, rifling was discovered and exploited during the American War of Independence.
To understand spin, an understanding of what's known as air speed and relative air speed is required.
Air speed: This is simply the speed at which an object moves through the air. A top pennants player can smash the ball at about 200 kilometers per hour. This is the speed of the ball relative to a stationary object (the table, the umpire's chair …, as long is it isn't moving, or else you start to get into the beginnings of Einstein's Theory of Relativity, which I'm NOT going into here). If the air itself is moving, then relative air speed is used.
Relative Air Speed: This takes into account any wind that the ball is traveling through. If for instance, you were to smash the ball (with an air speed of 200 km/hr) into headwinds of 10 km/hr, then the relative air speed would be 210 km/hr. If on the other hand you had the wind blowing behind you at 10 km/hr, the relative air speed would be 190 km/hr.
When wind occurs at an angle you introduce what's known as a vector term. This means the angle of the wind only partially affects the ball.
The mathematics is as follows:
