Dynamics of spin bowling: the normalized precession of the spin axis analysed with a smart cricket ball

As torque is imparted on a cricket ball before release, the spin vector precesses into the torque vector. Normalising the precession speed to the torque and the angular velocity yields the ‘normalised precession’, i.e. the angle between the spin vector and the torque vector. The maximal normalised precession was analysed in spin bowling, specifically in finger- and wrist spin, and topspin, sidespin and backspin deliveries. The data were recorded with a smart cricket ball and a Cortex motion analysis system. The maximal normalised precession at the beginning of the finger torque increased from topspin to backspin. The reason for this behaviour is that the motion of the bowling arm imparts a topspin on the ball, and therefore the spin axis does not have to change its direction if the fingers impart further topspin on the ball.