Do line call errors differ between men’s and women’s events in tennis? A case study from the 2021 Wimbledon Tournament

Line umpires make quick decisions. Ball trajectories and mechanical characteristics (velocity, spin) are different for male and female events, which can affect the decision quality. The aim is to analyse patterns of line umpire errors at the Wimbledon 2021 with a particular focus on differences between men’s and women’s matches. Data were obtained from the official match reports from 290 matches where the Hawk-Eye system was used to determine the umpires’ calls and used to calculate descriptive statistics and to run different linear regression models. Line umpires made 1 error per 17.7 games, with a mean error size of 30 ± 39 mm. Error size on long lines (18 ± 24 mm) was smaller compared to cross lines (40 ± 45 mm), which also served as a significant predictor in all regression models. In women’s matches, we observed a 7 mm bigger mean error size, which was in particular caused by a significantly bigger average error size for erroneous “out” calls (12.2 mm), which could be supported by the regression models. These results help to understand human decision-making performance on the grass. To improve line umpiring, we suggest to put awareness about the nature of line umpire errors, which indeed indicates that the task differs between men’s and women’s matches.