Characterisation of ball degradation events in professional tennis

Abstract

Tennis balls are acknowledged to degrade with use and are replaced at regular intervals during professional matches to maintain consistency and uniformity in performance, such that the game is not adversely affected. Balls are subject to the international tennis federation's (ITF) ball approval process, which includes a degradation test to ensure a minimum standard of performance. The aim of this investigation was to establish if the ITF degradation test can assess ball longevity and rate of degradation and determine if there is a need for a new degradation test that is more representative of in-play conditions. Ball tracking data from four different professional events, spanning the three major court surfaces, including both men's and women's matches were analysed. The frequency of first serves, second serves, racket impacts and surface impacts were assessed and the corresponding distribution of ball speed and (for surface impacts) impact angle was determined. Comparison of ball impact frequency and conditions between in-play data and the ITF degradation test indicated the development of a new test, more representative of in-play data, would be advantageous in determining ball longevity and rate of degradation with use. Assessment of data from different surfaces highlighted that grass court subjected the ball to fewer racket and surface impacts than hard court or clay. In turn, this appears to influence the distribution of ball speed on impact with the surface or racket, suggesting a surface-specific degradation test may be beneficial. As a result of these findings a new test protocol has been proposed, utilising the in-play data, to define the frequency of impacts and impact conditions to equate to nine games of professional tennis across the different surfaces.

The Effect of Ball Wear on Ball Aerodynamics: An Investigation Using Hawk-Eye Data

“…This tallies closely with other research, Lane et al found 318 racket impacts, on average, every 9 games [7], Figure 2 shows the distribution within the dataset. The aerodynamic performance of new and used balls was explored by examining first servesa relatively constrained delivery compared to open play.…”

“…Whiteside et al [6] examined metrics that distinguish between lower and higher ranked players in the Australian Open. Lane et al [7] looked for differences in ball performance during ball degradation. Wei et al used sophisticated modelling and statistical techniques to try to predict shot outcomes [8][9][10].…”

Measurement of Strain and Strain Rate during the Impact of Tennis Ball Cores

“…The 90 • and 30.5 m·s −1 impact condition was selected to include impacts at 90 • whereby the surface of the ball was tracked throughout impact as opposed to partially tracked. The impact condition representing the mean surface impact angle and ball speed found during professional play [1] was included to provide a benchmark against a more typical impact scenario. To determine the maximum absolute strain for each element of the surface, the major and minor strains of the element were compared to determine the greatest absolute strain value.…”

“…Four impact angles and five ball speeds were selected (Table 3), predominantly based on the findings of [1,2], to best replicate the impact conditions experienced during professional play. A maximum of five impacts per ball ensured minimal degradation in ball performance and, predominantly, ensured optimal pattern quality for the GOM software to process, as this could be inhibited by marks and smudges to the stochastic pattern.…”

“…Previous research assessing ball tracking data from professional tennis matches has established typical inbound impact conditions that the ball experiences, particularly when impacting court surfaces [1,2]. Knowledge of the impact conditions enables replication of typical impact conditions in the laboratory.…”