The professional tennis courts around the world literally emptied, leaving, only three protagonists in the singular (and five in the double): the players and the chair judge on his high chair. The technology has actually supplanted the line judges, deputies to call the ball “out”. From 2025 ATP and WTA, the two associations that protect tennis’s rights and organize most of the tournaments, have decided to do without them, giving full confidence to the “Electronic Line Calling Live”. In Slam, the Australian Open embraced the technological turning point already in 2021, followed a year later by the US Open, while this year it was up to Wimbledon to break a tradition that had lasted for 147 years. Roland Garros Parigino remains the only tournament in the major circuit that resists with the line judges.
The refereeing of a tennis match revolves mostly on “in” and “out” calls, that is, if the ball remains on the pitch (just touch the line) or not. Let’s find out together what science tells us about the margin of error of the human eye and technology.
What is the Hawk-Eye system and how the “Electronic Line Calling Live” works works
Elc Live was experienced for the first time at the 2017 Next Gen ATP Finals in Milan and was designed by an English company, Hawk-Eye (literally “hawk eye”), then purchased by the Japanese multinational Sony in 2001. Today many of the most popular sports use the Hawk-Eye system, the reason why the technology itself has commonly taken the name of “falcon eye”; A famous application is precisely the Goal-Line Technology in football, which relies on a similar system to determine with millimeter precision if the ball has passed the goal line.
In tennis it serves to draw the trajectory of the ball in the most realistic way possible. To establish if it is inside or outside, the image captured by a camera is not used when the ball lands, but are “triangped” (ie put together) the information of 12 goals. The latter, positioned in order to cover the whole field, manage to trace the movement of the ball to 340 frames per second and transmit it to a computer, which according to these data immediately makes a 3D projection of the point where the ball is about to fall. After elaborating the images, the system says to the high volume “Out!” When the ball is out, replacing, even “vocally”, to the line judges. In an interview with the CNBC, the British company explained how the equipment for a tennis court cost about 100 thousand dollars and that it usually takes three days to install and calibrate it. It is done by pulling the balls several times on the lines, with a racket or a shooting-pallline car.
Margin of error in tennis: the numbers of the human eye and that of the “hawk”
We come to the edge of error and the comparison between the human eye and that of the “hawk”. An American study from 2008 has estimated that the line judges are missing 8.2% of decisions when the ball, which can travel at speeds above 200 km/h, falls in an area to a maximum of 10 centimeters from the line. The electronic system, on the other hand, was put on the market with a margin of error between 2.2 and 3.6 millimeters, equal to 1%. The numbers therefore show a clear supremacy of the hawk eye in real time compared to the decisions of the line judge, also influenced by psychophysical variables such as stress or vision defects or, in general, by external distractions.
Red earth is a separate case
The Roland Garros, or the only slam on beaten earth, remains the only tournament of the major circuit that still adopts the human judges, but the other events on the red, such as the International of Rome, albeit with delay compared to the competitors on grass and concrete, have chosen the technological way since 2025. This created many controversy among the players, primarily the German Sascha Zverev and the N ° 1 of the world Aryna Sabalenka, who in recent months, armed with smartphones, have not thought twice and have published the errors of the hawk on social networks. Yes, because the red earth is the only surface showing the signs of all the blows and, by the regulation, the judgment of Hawk-Eye is unquestionable. Translated: even if the royal imprint shows the error of technology, the chair judge cannot change the decision.
One of the reasons why tournaments on red earth have delayed the use of technology is that the surface is more changeable, it changes according to the weather conditions (it can be humid or dry, swept by the wind or not) and the passage of the players. This slightly increases the margin of error, and above all it makes a more frequent recalibration necessary. In the tournaments on concrete, this is made only at the beginning of the event, while on earth it should be adjusted even between one game and another, in one operation that would require about half an hour, a difficult practice in a dense programming of matches.
Foxtenn, a fox challenges the eye of Falco
Over the past few years another player has been included in the market of arbitration technological support and movement: the Spanish company Foxtenn. The system was approved at the end of 2016 following a rigorous series of tests and criteria established by a committee made up of representatives of ITF, ATP, WTA and the Grand Slam tournaments. Using about 40 cameras, scanners and laser, Foxtenn captures the rebound of the ball on the field in real time, eliminating the need for simulations and boasting an error rate of 0 thanks to over 150,000 images per second. Several minor tournaments have adopted the Foxtenn system, especially on the red earth where the ball leaves, as mentioned, a physical sign, but among the disadvantages there are high installation costs.
