The John McEnroe Effect can be loosely described as the discrepancy in perception between tennis players and line judges when it comes to viewing the way a tennis ball travels along the line.

This "phenomenon" was made popular with the controversial way the said tennis player would argue with the judges when making the proper line calls on the court.

A recent study was conducted which tested the accuracy with which tennis players and judges would perceive line call errors while matching them up against other laboratory data. It was shown that observers tend to see moving objects slightly ahead of their actual position.

It was also discovered that both parties can more or less call the bounce position of a ball moving at up to 50 meters per second within just a few centimeters. However, some errors were inevitable due to limitations in perceptual processing in the brain.

Professor George Mather of Sussex University, a psychologist specializing in motion perception in lab-based experiments, had this to say regarding the results of the study taken from the data on the Hawk-Eye electronic line call adjudicator device that was used:

When a ball bounces very close to a court line, the brain is unable to locate its position with sufficient precision to reach a correct decision on every occasion, so both players and line judges make some errors. Line judges, however, are more accurate than players. Nevertheless, both players and judges are remarkably accurate.

It was interesting to see that line calls on base and service lines tend to be more difficult than those on side and center lines. Mather mentioned that, according to the data, up to three line call challenges made by players during a set "seems fair".

It's still unsure whether John McEnroe would have won more Wimbledon tournaments given the results of this analysis, but it definitely sheds some insight into how the physics of tennis can be a rather exact science.