Sunday, May 30, 2010

The "gyro ball" variation for the off-spinner/ left arm orthodox bowler

It is fun to imagine new kinds of bowling delivery, and the gyro ball is the name I give to what may or may not be the main variation deployed by Graeme Swann.

It gets the name because it rotates on a vertical axis, rather like the children's toy called the gyroscope.

Like an off-spinner's off-break, the ball is spun from using the index finger with the seam gripped between index and middle finger; but the axis of spin is vertical, and the seam rotates towards the right-handed batsman on the leg side and away from the batsman on the off side.

This means that the gyro ball will swing away from the right-handed batsman, and this away movement will probably not be affected when the ball pitches because it will not grip on the pitch.

So the gyro ball is actually a kind of spun away-swinger.

The reason it swings the way that it does is that as the ball is travelling towards the batsman, the air flow over the side spinning towards the direction of travel will be higher than the pressure on the side of the ball spinning away from the direction of travel.

In effect, the ball spinning away from the direction of travel can be imagined as pushing the air backwards behind the ball more quickly, reducing its pressure; while the side of the ball spinning towards the direction of travel could be imagined as pushing against the air as is goes past and slowing it - thereby increasing its pressure.

This is why top spinners dip, and back spinners (sliders/ flippers) float, and why an over-spun off-break (with the seam at 45 degrees to the wicket) will both dip and swing away.

The 'big spinner' bowler could therefore, in theory, angle the spinning seam to produce various combinations of dip, float, and away swing - while all the time spnining the ball hard (and therefore making mis-hits much more likely than when bowling non-spinning variations - such as the traditional away-swinging 'arm ball').

{The above applies to the left arm orthodox slow bowler - reversing all the directions and rotations as appropriate - such that the gyro ball would become an inswinger to the right-handed batter.)