Technology is changing and so too is how many sports are regulated. In recent years, tech, like video-assisted refereeing in soccer and basketball, wearable sensors used to track one’s performance, and the Hawk-Eye camera system used to track ball movement across numerous sports.

This article focused on the latter – Hawk-Eye – and how it has impacted the game of tennis. We explore many of the most frequently asked Hawk-Eye questions and answer them to the best of our abilities.

9 FAQs About Hawk-Eye Ball Tracking Technology

Here are several of the most common questions tennis fans have about Hawk-Eye.

#1 What is Hawk-Eye?

Hawk-Eye is a computer vision system used in many sports, including cricket, tennis, Gaelic football, badminton, hurling, rugby union, association football, and volleyball. It visually tracks the trajectory of the ball and displays a moving image profile of its statistically most likely path. The onscreen representation of these trajectory results is called Shot Spot.

Normally positioned on the underside of the stadium roof, at least six high-performance cameras work to track the ball from different angles.

A three-dimensional representation of the ball’s trajectory is created by triangulating and combining the video from these six cameras. Advertised to be accurate within 3.6 mm, Hawk-Eye is not infallible but is generally trusted as an impartial second opinion in sports.

#2 Who Invented Hawk-Eye?

Developed in the United Kingdom by Paul Hawkins, the Sony-owned Hawk-Eye system was originally implemented for television purposes in cricket in 2000.

#3 Which Sports Utilize Hawk-Eye?

Governing bodies in tennis, cricket, and association football have accepted it as a means of adjudication with a different number of cameras depending on the sport.

Since 2006, Hawk-Eye has been used for the Challenge System in tennis and for the Decision Review System in cricket since 2009.

For the 2013–14 Premier League season, the system was rolled out as a means of goal-line technology. In December 2014, it was adopted for the 2015–16 Bundesliga season as well.

#4 How is Hawk-Eye Used in Tennis?

All Hawk-Eye systems are based on the principles of triangulation, using visual images and timing data provided by high-speed video cameras located at different angles and locations around the play area. There are 10 cameras for tennis.

The system processes the video feeds from the cameras and ball tracker rapidly. A data store, which includes data on the rules of the game, contains a predefined model of the playing area.

In each frame sent from each camera, the system identifies the group of pixels that corresponds to the image of the ball. It calculates for each frame the position of the ball by comparing its position on at least two physically separate cameras at the same instant in time.

A succession of frames builds up a record of the path along which the ball has traveled. It also predicts where and how it will interact with any features within the playing area already programmed into the database, forecasting future flight paths. The system can interpret these interactions to decide if there have been infringements of game rules as well.

#5 Why the Urge for Electronic Line Calling in Tennis?

In Serena Williams’s quarter-final loss to Jennifer Capriati at the 2004 US Open, three line calls went against Williams in the final set while the Auto-Ref system was being tested during the match. Though the calls were not reversed, there was an overrule by chair umpire Mariana Alves of a clearly incorrect call by a line umpire that TV replay showed to be good.

These errors prompted talks about line calling assistance, especially since the Auto-Ref system, which was being tested by the U.S. Open at that time, had shown high accuracy.

#6 When Was Hawk-Eye First Tested by the ITF?

In late 2006, the International Tennis Federation (ITF) tested Hawk-Eye in New York City, and it was approved for professional use. Hawk-Eye revealed that during the tests in New York, 80 shots were measured by the ITF’s high-speed camera, which is a device similar to MacCAM.

At an early exhibition tennis tournament test of the system in Australia, there was a moment when “Out” was shown as the call for a tennis ball but “In” was what accompanied it. This mistake happened because the tennis ball appeared as a circle instead of an ellipse on the graphical display. The incorrect call was fixed right away.

#7 How Does Hawk-Eye Improve Tennis as a Sport?

Hawk-Eye does not improve an individual’s performance, but it helps judges and also enhances spectator appeal. It enables players to contest close line calls by forcing the umpire to call upon Hawk-Eye for a second opinion on whether the shot in question was in or out.

While it may have some flaws that will no doubt be worked out over time, the Hawk-Eye system has greatly contributed to tennis. The Hawk-Eye system’s introduction has added a new level of strategy to the game of tennis that never existed before. Since players now only have access to three challenges per set, they must be wise about when to use those challenges.

Having the power to challenge any call you please is very tempting, especially in this sport, but patience is still a quality that will lead to success in tennis. In addition to knowing when to use a challenge, a player could also burn a challenge, possibly slow their opponent’s momentum, and regain composure during the time it takes for the call to be reviewed should they find themselves in a tight spot.

The Hawk-Eye system has also helped to improve fan involvement at major tournaments. Spectators, whether they are in the arenas or watching from home, simply love the drama and strategies that the challenge system has introduced. Every single challenge displayed on the giant video screens in stadiums is met with fans reacting as the animated ball travels through the air towards the line.

If you have ever witnessed such an event, then you would have noticed how the result of a challenge is never immediately revealed either. Instead, there’s a delay after the animated ball strikes the digital court on screen; then suddenly, as the view of court rotates, and “In!” or “Out!” flashes on screen adding to fans’ excitement.

The Hawk-Eye system not only boosts current sport fans’ enjoyment but also adds an exciting new element to attract future fans.

#8 What are Hawk-Eye’s Known Issues?

The issue with devices that reconstruct tracks is that their output relies on estimates. In any one frame, the position of the ball appears as a blob of pixels. If the ball is swerving, its future path must be extrapolated from at least three frames; however, if it’s moving fast and near to the crucial impact point is its bounce point, there might not be three frames available.

Even with three frames, projections have errors, and if the ball distorts on impact as in tennis, the footprint on which the line call is based is again the result of an inexact calculation – and so on. Hawk-Eye itself used to claim an average error of 3.6 mm; more recently, it claims this has been improved to an average of 2.2 mm.

However, particularly in tennis, this margin of error isn’t reflected in the replays because of the reliance on this technology to provide a definitive call, leading most fans to assume it is 100 percent accurate.

Of course, accuracy will depend on the speed and the angle of the ball, as well as many other factors. This is why these figures are average, and, just like with all averages, sometimes the error can be much bigger – occasionally even significantly so. To understand what is happening, one needs details of the tests and the distribution of errors that occurred.

#9 Do Pro Tennis Players Appreciate Hawk-Eye?

The relationship between players and judging officials, always strained, is not new to those familiar with this sport. It’s no surprise, then, that a vast majority of players would support such technology. The implementation of the Hawk-Eye system into their sport is viewed as something positive and exciting by many past and present players. As they are the ones most affected by its use, the opinion of the players is by far the most important.

When asked about his thoughts on the Hawk-Eye system, tennis legend Andre Agassi said that in 20 years of professional tennis, this is one of the most exciting things to happen for players, fans, and television viewers. Adding that this new technology will add a whole new dimension to the game.

Most veteran players have been quoted saying that they wished they had such technology to use when they played the game. Andy Roddick was also quoted making comments about how he relished the opportunity to embarrass judging officials.

Even though the vast majority of tennis players favor using Hawk-Eye, there are still some bound to be against it. In this case, the two leading voices against this technology also happen to be the world’s two best players. Both Roger Federer and Raphael Nadal have made it very clear that they do not appreciate adding the Hawk-Eye system to their sport.

Due to Federer and Nadal’s positions as two of the greatest players in the world and their winning records, these two players’ opinions have carried some weight.

It is clear that Roger Federer does not see things the way Andy Roddick does. His main point arises from the previously discussed problem regarding how judging officials are now hesitant to make calls in matches. He also does not believe this technology is accurate, is extremely reluctant to use it and frequently requests that it be turned off for his matches.

Raphael Nadal has had quite a different experience with the Hawk-Eye system, which has been the source of his disdain for the technology. At the Dubai Championships in 2007, Raphael Nadal was playing against Mikhail Youzhny when a controversial moment involving the Hawk-Eye system emerged. When Youzhny hit a shot that Nadal believed to be out but Hawk-Eye ruled was in, Nadal became enraged.

In Closing

Has the Hawk-Eye system improved the game of tennis? Yes, is the answer to this question. The Hawk-Eye system has greatly improved the game of Tennis by adding new levels of strategy for players, increasing fan engagement, and helping to resolve major disputes on court.

Although there are some issues with the system, over time they will be resolved and using Hawk-Eye will become more seamless. The arguments and opinions of those opposed to using the system represent a minority viewpoint; as technology evolves, these arguments lose their validity.

While tennis is a sport with much tradition; Hawk-Eye poses no threat to those core values being disrupted.