HOW DO PROFILES AFFECT BALL PACE AND BOUNCE?

Pace is the speed at which the ball comes off the pitch and bounce is the height of the ball as it passes the batsman. The profile affects the ball pace and bounce in a number of ways. Although cricket balls seem hard, they are compressible – that is they flatten and recover (most of) their shape on collision with the surface. This is why the ball bounces –as it lands it flattens storing energy, which is then released as the ball recovers its shape. Slow pace occurs when energy is absorbed by the surface during ball impact and is not returned to the ball as it leaves the surface – effectively the pitch acts as a shock absorber.

Generally there are four reasons why a surface (pitch) will deform on impact:

1. The pitch is also slightly elastic in that it deforms and recovers during impact – this is a very small contribution to ball bounce, most of it comes from the ball.

2. When a pitch is wet, it will deform around the ball permanently – you see this as a pitch mark on soft wet pitches. Energy has been transferred from the ball to deform the surface but has not been returned so pace and bounce are reduced.

3. Thatch layers allow the surface to deform – although thatch seems ‘springy’ it is a relatively slow deformation so it does not recover before the ball bounces away – this can make pitches low (ball bounce) and slow (pace).

4. Horizontal root breaks mean that the surface layer is detached from the rest of the profile and separated by deformable roots. These behave a bit like the thatch layer above.

Well prepared, hard pitch with a good profile

In this example, as the ball impacts with the surface, there is only very small deflection of the surface causing the ball to compress – storing the energy of the impact in the ball. As the ball rebounds from the surface the surface rebounds returning its energy to the ball and the ball recovers its shape, meaning that there is maximum energy returned to the ball during rebound, maximising pace and bounce.

Profile with thatch

In this case as the ball impacts with the surface there is a larger deflection of the surface meaning more enrgy is transferred to compressing the thatch. Although the thatch is elastic and will recover – it does this relatively slowly and by this time the ball has gone. This reduces the energy stored in the ball and transferred back to the ball, slowing it down and potentially reducing bounce. Excessive thatch will lead to low-slow pitches.

Profile with a horizontal root break

This is very similar to the thatch problem in that the roots and the surface layer will move. The movement is not as large as the thatch example but the recover is still relatively slow, meaning that energy is lost during the ball impact and that the pitch becomes lower and slower. The other thing about root breaks and thatch is that they are rarely uniform across a pitch and this can lead to variation in pace and bounce.

These examples show how pitch profile is critical in ball bounce. Identifying pitch problems and taking the right steps to rectify them can help pitch performance.

Return to: STAGE 1: LOOK FOR THE FIRST SIGNS OF PROBLEMS