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In Defense of Ball Marks: Why Hawk-Eye on Clay is Unnecessary

Since Hawkeye was introduced in tennis in 2006, it has taken on an air on invincibility. How many times has a commentator erroneously proclaimed that a player should challenge, emphatically convinced from their position in the booth that the call is incorrect? As much as John McEnroe would hate to hear it, officials are more accurate than the punditry give them credit for.

The technology? Not so much.

ITF rules state that any review system must be able to judge a ball in or out within a five millimeter margin of error (0.20 inches). Incorrect calls are fine, so long as they are not wrong by more than 10 millimeters (0.40 inches). Paul Hawkins, the godfather of Hawkeye technology, said that its margin of error of the current system averages about 3.6 millimeters (0.14 inches). The standard diameter of an ITF approved tennis ball is 67 millimeters; mathematically, Hawkeye has a 5 percent margin of error as it relates to the ball.

Hawkeye is not a live picture, nor is it accurate representation of the ball hitting the court. At its core, Hawkeye is an “officiating aid”; it is not meant to completely replace the role of on-court officials. It is nothing more than a digitally-generated representation of court conditions and where the ball landed based on its trajectory off the racket. It’s no coincidence that the marks on Hawkeye replays look very similar to each other, regardless of what type of shot is being challenged. On clay, the mark is an actual representation of the ball hitting the court. Each ball mark will look different based on what kind of shot was hit, whether it be a lob, overhead, etc. Occasionally, there is an argument about a ball mark or reading from the chair umpire, but in the grand scheme of things, it doesn’t happen very often at all. One misinterpretation might be beaten to death, but it doesn’t actually mean it’s an epidemic. Even though the occasional ball mark will be misread by the umpire, the risk of that is statistically far lower than a margin of error of +/- 3.6 millimeters on every ball.

In a sense, implementing Hawkeye on clay would be ‘put up or shut up’ time for the technology and its manufacturers. The mark never lies and players, officials and fans can finally see for themselves how many calls were upheld or overturned when they really shouldn’t have been. Set the scene for the worst case scenario, and a very plausible one. Rafael Nadal and Novak Djokovic are playing in a Roland Garros final, late in the fifth set. Nadal’s shot is called out on a break point for Djokovic, and Nadal challenges. The technology rules the ball in, but there’s a clear mark showing that it is in fact out. There’s no evidence to suggest that the technology is more accurate than the mark, so what’s right? That might be an extreme example but a valid, and very real, concern. The chair umpire’s hands are tied and control over the match is more or less taken out of his or her hands. On the other side of the coin, the credibility of the technology as a whole take a hit. What happens then?

So why has Hawkeye passed the test for accuracy on hard and grass courts and not clay? Briefly, the ball does not leave a discernible mark that can be read on either of these surfaces. On a hard court, Hawkeye cuts down on arguments because players recognize that the mark there is not always the full representation of the ball. In addition, the lines are painted on both these surfaces; they’re flat, and allow for Hawkeye to gauge a more accurate reading. The lines on clay are not even. This is another one of the biggest reasons why Hawkeye on clay can’t work.

“We decided not to use Hawk-Eye on clay because it might not agree with the mark the umpire is pointing at,” now-retired chair umpire Lars Graff said in 2009. “Most clay courts now have embedded concrete lines that sit a millimetre above the surface. This means that a ball that nicks the line, and therefore is in, does not show up on the clay but would show up as ‘in’ on Hawk-Eye. That would cause a problem.”

The same goes for “Hawkeye” that’s in place for television replays. It’s not an official review and used for nothing more than the entertainment of the television viewing audience. If the technology hasn’t been authorized for official use on the surface, and its accuracy on the surface called into question, it’s irresponsible to even be showing these kind of replays.

An example: In a match between Jo-Wilfried Tsonga and Juan Monaco at the Monte Carlo Masters in 2011, Tsonga hit a serve that was wide of the center service line which was called out by the line umpire. The chair umpire came down and inspected the mark and agreed the serve was out. Tsonga agreed with the ruling. A view of the mark on the clay was then shown, and it was clearly out.

They then showed the unofficial Hawkeye image, which was just touching the line.

If some kind of electronic review is to be implemented on clay, an entirely new system would need to be developed. While Hawkeye is a great tool, it has its flaws and has no place on clay in its current form. Reading ball marks on clay has nothing to do with the ‘purity of the game’ or ‘being stuck in the past.’ No one should be convinced that a Hawkeye replay is actually more accurate than reading a ball mark. Until the day comes that Hawkeye has zero margin of error, it won’t be. It’s simple math.

“As a player, you love Hawkeye,” Mike Bryan said earlier this week at Roland Garros. “You know that it’s right on.”

But is it?

About Victoria Chiesa (113 Articles)
One time, Eva Asderaki told me I was lovely. It was awesome. @vrcsports

6 Comments on In Defense of Ball Marks: Why Hawk-Eye on Clay is Unnecessary

  1. (Pre-comment: I agree with your general conclusions)
    That Lars Graff comment doesn’t make a lot of sense. If that ball is in, and Hawk-Eye will show it as in, where’s the problem? Is he saying that balls that skid off the line today might be called out by umpires?….


    • unseededandlooming // June 3, 2013 at 8:22 am // Reply

      I don’t think he’s saying that. It confused me too, but my interpretation was that he’s trying to draw a parallel between being able to validate the in call via a visible mark. If a ball skids off the line and Hawkeye calls it in, great. But I think he’s saying there’s some instances where that would be misread by the technology, supporting the idea of its inconsistency; if a ball hits the line, nothing shows up on the court, and umpires are trained to read that. In that instance, there’s nothing Hawkeye can track.

      It’s more about the lines being raised over the surface and how that relates to the accuracy of the machine than anything else.


      • Thank you for posting my previous reply. and thanks for the great quote from Lars and the link to the article. But I interpret his words differently than you and Anna. Look at the end of Lars’ comment:

        “… This means that a ball that nicks the line, and therefore is in, does not show up on the clay but would show up as ‘in’ on Hawk-Eye. That would cause a problem.”

        He’s making two points. Most important, having Hawk-Eye show a different result than the ball mark would cause argument and distract from the tennis. The secondary point is that Hawk-Eye would actually be correct in the case where the ball skipped off (nicked) the edge of the line and left a clay mark on second impact. Might have been clearer if he said “…and therefore is in, but does not show AS IN on the clay…”

        I think his judgment was sound. The tennis community wouldn’t have been able to accept a Hawk-Eye result that differed from human sight.

        There’s a good Hawk-Eye write-up at:

        Hawk-Eye doesn’t evaluate the ball mark, but uses 10 cameras to calculate the impact from the flight of the ball.


  2. Mr Hawkins says that the margin of error of his Hawk-eye is 3.6mm. Thank you but as long as I haven’t seen the metrologic report from an independent testing company, I have absolutely no reason to believe him. I understand that he wants to sell his product and I understand that some players, probably due to their lack of scientific background understand nothing about this issue. Maybe we should start informing them that the image of the circuit court in the machine and the circuit court itself are not the same. Lines are never perfectly parallel or square in reality..


  3. The chair umpire can select the wrong mark. Either relying on the mark that a player circles (a players wouldn’t try to cheat, would they?), or asking the line umpire (whose call is being questioned) where the mark is.

    Here’s a compromise that (technology willing) might be more acceptable.
    Use Hawkeye to ensure the umpire is looking at the correct mark. The umpire could have a handheld device that gets the Hawkeye info and leads (within 4mm) to the mark in question. The device could even take a picture of the mark so we can see how they interpret the mark. Did you see Cedric Maurier’s call against Troicki?


  4. Thanks for finally talking about >In Defense of Ball Marks:
    Why Hawkeye on Clay is Unnecessary | unseeded & looming <Loved it!


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