# Hawk-Eye Line-Calling System

Hawk-eye is a technology used in tennis for determining if the ball is in or out. This line-calling system uses multiple camera angles to trace the tennis ball's trajectory. Hawk-Eye uses six or more computer-linked television cameras situated around the court. The computer processes the video in real-time, and tracks the path of the tennis ball on each camera. These six separate views are then combined to produce an accurate 3D representation of the path of the ball.

## Hawk Eye History

The Hawkeye system was invented by a young British computer expert Paul Hawkins, and was launched in 2001. It was first used in television coverage of sporting events such as Test cricket, and has now reached the stage of being used by officials in tennis to assist in adjudicating close line calls.

The Nasdaq-100 Open in Miami was the first tour event to officially use the technology. The 2006 US Open was the first Grand Slam event to feature the system, followed by the 2007 Australian Open.

In 2020, in response to the need to reduced the number of people on the court, the U.S. Open tennis tournament replaced human line judges on 15 of 17 match courts with Hawk-Eye Live, an advanced system that makes automated line calls in real time. This Hawk-Eye Live system features 18 cameras, six of which are used by a review official to monitor foot faults. The system uses recorded voices to make its calls, which shout "out," "fault" or "foot fault." The courts using Hawk-Eye Live at the U.S. Open will have only a chair umpire to call the score after the system makes the call, and they will take over only if the system malfunctions.

Is the ball in or out?

## Rules

The current rules under which Hawk-Eye is used:

• Each player receives two challenges per set to review line calls.
• If the player is correct with a challenge, then the player retains the same number of challenges. Effectively they have an unlimited number of correct challenges to make.
• If the player is incorrect with a challenge, then one of their challenges is lost.
• Challenges may not be carried over from one set to another.

## Results

Players have said that they instinctively know when a ball is in or out, though based on their use of the review system the evidence so far has not been conclusive. One analysis of the player challenges that have been made found that they were correct only about 46% of the time.

Officials of the French Open have so far refused to take up the technology, saying that the unique characteristics of the clay court do not warrant it. As the ball makes a mark on the clay surface, it is possible for the chair umpire to get out and have a look at the mark to determine if the ball was in or out, thus avoiding the need for hawke-eye.

Anyone who has watched a match on TV where they have used this system may have noticed that the ball seems to be elongated when projected on the court surface. This may be explained by imagining the ball hitting the ground with a lot of topspin, that it actually spins forward when in contact with the ground and is deformed so much as to flatten on the ground. The mark doesn't have to have the exact surface area of the cross-section of the ball to accurately represent the impact point of the ball.

## Related Pages

• Hello....what is not clear is when the score is amended for a correct challenge, or whether the point is re-played. I have noticed that both of these options are used by umpires. Mike Padmore (2013)
• It depends on the situation. If an out call is made but upon review it is seen that the ball is good, the point is replayed. If the ball is called good but upon review it is seen to be out, the point is awarded and play resumes. Clash14 Mike Padmore (2018)
• How was Wasinowski able to successfully appeal the result of Hawkeye decision that clearly showed her shot was out? Mike Friend (2019)
• Why is the projected ball once it hits the ground displayed as an ellipse in 'Hawkeye'? (the ball is spherical) - Jan van mourik (2017)
• I think it is because the ball physically flattens when it hits the ground, and this shows on the camera view. When you hit a really hard serve, for example, into a fence, the ball will deform and sometimes will go through the chain-link fence. If it stayed 'spherical', it would not go through. Just my thoughts. :) The article explains this a bit also: "This may be explained by imagining the ball hitting the ground with a lot of topspin, that it actually spun forward on the ground and deformed so much as to flatten on the ground." Andrew Kaczrowski jan van mourik (2017)
• The Hawk-Eye line calling system is flawed and needs to be retired from all tennis tournaments. Frequently the system depicts a tennis ball in an oval shape when it hits the tennis court. You would need to stand on a tennis ball to get it to touch the court in an oval shape. Only a small portion of the bottom of a tennis ball will depress before it bounces back up. We used to use real cameras back in the day for line calls and the camera doesn't lie. All previous camera shots showedthat tennis balls retain 95% of their shape. So, this system has been making false claims for years without anyone questioning its validity. All service, baseline and sideline calls have been elongated and distorted beyond natural occurrences. In reality only the bottom of the round tennis ball actually hits the court. The side circumference of the ball never hits the ground. So, all these oval CGI (Computer Generated Images)are the computer operator trying to fix the match in one or another opponents favor. This is simply illegal and needs to be stopped immediately. I believe that going back to high resolution cameras would be the best alternative to the flawed Hawk-Eye system. TK Andrew Kaczrowski (2017)
• You do realise hawk-eye uses at least 6 extremely high resolution cameras don't you? R TK (2019)
• This is just plain wrong. The shape of the area of impact depends on a number of factors, including the velocity, angle, and spin of the ball on impact, as well as whether the ball skids. This is partially explained above. But if you need proof, just look at the marks left on a clay court... they are usually oval-shaped and sometimes quite elongated. Rumple Frumpery TK (2019)
• To help clarify this, the ball depresses slightly when hitting the ground and also continues its forward motion by turning or sliding until it leaves the ground. It's shape is therefore determined by these and other factors mentioned by Rumple. Richard Krasilovsky Rumple Frumpery (2019)
• The problem with clay is that the mark remains after impact. However if a previous shot had made that dent how can u be sure that the ball is in or out??. Hawk eye is crucial to the French Open and all clay court surfaces. Nathan (2014)
• Will they get a point if there call is correct or it will remain constant??? Anil Sapkota (2013)

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