Analysis of errors made by line umpires on ATP tournaments

This is the first study in this field investigating the number and extent of line umpires' errors during two international, Association of Tennis Professionals (ATP) Masters 1000 tournaments. Hawk-Eye technology was used on these courts, allowing players to challenge line umpires' calls. The goal of the study was to determine line umpire error rates for calls reviewed by the Hawk-Eye system. We subsequently determined the mean size of errors and analyzed these errors on specific court lines. Data were obtained from official records of the Hawk-Eye system in selected matches and were provided by ATP. Results showed that line umpires made errors in 27% of cases where Hawk-Eye review technology was utilized. This means that an umpire error occurred once per 17.4 games. The mean size of line umpires' errors reached 33.2 mm. Most errors occurred at the baseline. A difference in the number and size of errors between cross (transverse) and long lines was found, which suggests that the results for long and cross lines should be treated separately in the evaluation of line umpires' performance. The line umpires made fewer and smaller mistakes towards the end of a tournament in comparison to its beginning. It is misleading to evaluate line umpires' performance in %. We suggest that the coefficient 1 error per N games should be used instead.