The Biomechanics of Line Calls Or How to Keep Your Friends

 Part 1

One day all elite athletes will have their Dynamic Visual Acuity checked and improved.  Until that day, all I can do is present evidence of how important it is and how limited the human eye is in the hyper fast, hyper difficult world of tennis.

Part 1 is an astute investigation of the science and practice of professional line calling.  An article that helps describe how difficult a task tennis presents for the human eye.  Incredibly, this is just for the poor linesmen who are sitting still trying to focus on one bounce of the ball in one spot.  Linesman are actually told to NOT watch the ball!  Wow!

In stark contrast to this trained professional linesman, most line calls in our sport are made by players who are running, out of optimal position, and probably feeling obligated to their doubles partner.  No wonder the demands can get out of control and cause friction among friends!

Part 2 is an article to help put the Part 1 description into practical application for your tennis.  The pros now have the benefit of Hawk Eye technology, the rest of us do not.  Hopefully, these articles will help you find the proper perspective on your next line call.

~Best of luck with your tennis!


By Alan Schwarz
Published: June 23, 2009,

When a line judge at Wimbledon rules on a hair-splittingly close call and says the ball is out, the inevitably disgruntled player should not only consider challenging the call for review by digital replay system. He should consult a recent issue of Current Biology.

A vast majority of near-the-line shots called incorrectly by Wimbledon line judges have come on balls ruled out that were actually in, according to a study published in October by researchers at the University of California-Davis. To the vision scientist, the finding added to the growing knowledge of how the human eye and brain misperceive high-speed objects. To the tennis player, it strongly suggests which calls are worth challenging and which are best left alone.

The researchers identified 83 missed calls during the 2007 Wimbledon tournament. (Some were challenged by players and overruled, and others were later identified as unquestionably wrong through frame-by-frame video.) Seventy of those 83 calls, or 84 percent, were on balls ruled out — essentially, shots that line judges believed had traveled farther than they actually did.

Called perceptual mislocalization by vision scientists, this subconscious bias is known less formally to Wimbledon fans as “You cannot be serious!” — John McEnroe’s infamous dissent when, yes, a 1981 shot was ruled out. Now that players can resort to a more evolved appeal procedure, the researchers’ discovery suggests that players should generally use their limited number of challenges on questionable out calls rather those that are called in, because such out calls have a far better chance of being discovered as mistaken on review, then overturned.

“What we’re really interested in is how visual information is processed, and how it can be used to a player’s advantage,” said David Whitney, an associate professor at U.C.-Davis’s Center for Mind and Brain and the paper’s lead author. “There is a delay of roughly 80 to 150 milliseconds from the first moment of perception to our processing it, and that’s a long time. That’s one reason why it’s so hard to catch a fly — the fly’s ability to dance around is faster than our ability to determine where it is.”

This is the third Wimbledon in which players can challenge questionable calls for review by the Hawk-Eye system, which uses high-speed video cameras to record balls’ flight. (About 25 percent of all challenges result in overturned calls.) There is no cost to the player when a call is proved correct, but after three such episodes in a set a player may not challenge again. Whether through strategy or residual tennis etiquette, most players leave many challenges unused.

Theoretically, line judges should be equally prone to call an out ball in as they are an in ball out. But when objects travel faster than humans’ eyes and brains can precisely track them — for example, Andy Roddick’s 150-mile-per-hour serves — they are left having to fill in the gaps in their perception. In doing so they tend to overshoot the object’s actual location and think it traveled slightly farther than it truly did.

Both successful challenge calls as well as the overlooked mistakes that the researchers later identified were several times more likely to come on “long” calls than “in” calls. (The same pattern existed at Wimbledon last year, Whitney said, although the paper did not present that data.) So players are better off using as many challenges as possible on balls called out, because those are the calls most likely to be wrong; if a player thinks an “in” call was wrong, chances are his own eyes were as fooled as line judges’ sometimes are.

Without knowing it, tennis officials are already told to try to compensate for this mislocalization effect. Published instructions for United States Tennis Association line judges tell them to “focus your eyes on the portion of the line where the ball will land,” rather than attempt to track the ball in flight. “Get to the spot well before the ball arrives,” they are advised.

Rich Kaufman, the association’s director of officials and a linesman and chair umpire from 1976 to 1997, said that of all things “one of the hardest things to teach new linesmen is to take their eye off the ball.”

“I once asked an eye doctor, then what am I seeing on a bounce?” Kaufman said. “The doctor said that’s your brain working — you think you see the initial point of impact but it’s the blur of the entry and exit of the ball.”

A player using his knowledge of this effect in challenging calls could see a benefit of about one or two overturned points per match, Whitney said, plus any psychological boost from feeling vindicated rather than robbed. But Whitney added that understanding how the brain misperceives visual stimuli can help in more real-life matters, like the design and placement of high-speed safety equipment, automobile brake lights and warning signs of all types.

As for Wimbledon, it appears as if the new information can only help players, not the judges who vex them. Kaufman said: “You have to call what you see. Or what you think you see.”

Part 2


by Jonathan Bailin, Ph.D.

Over the years, I have addressed this issue verbally with recreational players from time to time.  It is
so important to them however, that it should be placed here for future reference….

Strong, successful personalities often treat recreational tennis as just another litmus test of
their personal success.  That their competitive nature in business should be reflected in all arenas
of their lives.  Why not tennis?

Because by definition, it is “recreation”.  An important word to keep in mind on court.

I hope you have had a chance to look at the above article on eye skills and line
calling I reproduced from the NY Times.  VERY RARELY are bad line
calls on purpose in amateur tournament tennis, and practically never in social tennis.
That said, they are an ever present artifact of imperfect eye sight for all players and officials.

It’s clear that some players become hypersensitive to line calls in general, but a more “recreational”
and relaxed approach to this situation is in order.  Here is an adult, big picture approach:

No one wants our favorite sport to have any adverse effect on our friendships.   Recreational
players are important cogs in each others social wheel.  Your goal should be to have many years
of amicable social and competitive tennis ahead, with all players available, at your skill level.

====>  To that end, I propose you use a new line call policy on court– If an opponent even looks at you
funny after you make a call, give the point away!  <======

This can be confusing and difficult at first, but it is an important response for all tennis players.

First, admit to yourself that if you are not making a living on tour, no matter what “competition”

you are engaged in, you are playing “social tennis”.  That is you are in a very small, tightly knit

community which communicates frequently about ALL aspects tennis.  More important than any

trophy or team success, your reputation as a mature person, who others enjoy playing with, is at stake.

Social tennis should test skills, not reputations, because tennis should not be at that

level of importance in our lives.  Your business, your family, your contributions to the people

around you, the planet, and your health are that important.  Not tennis!

In my professional opinion, suggesting to “Replay the point” is not a strong enough gesture of capitulation to
an opponent who has just taken a risk by questioning a call verbally or by body language.  Keep
in mind that they already feel awkward.  Your choice is to help them relax by showing an expert
understanding of the situation or heighten their fears that they will face ridicule or rejection.

ALL PLAYERS SHOULD RESPOND TO THAT SITUATION BY– asking for their help in making the call “if you saw it more clearly than I did” and graciously, with genuine intent, offer them the point.  Let THEM offer to play the point over and do not offer that option yourself.  If you are going to capitulate graciously, go the whole way!

This does several things.  One, it demonstrates that you understand the challenges for the human eye.  Two,
you are mature enough to have your priorities straight in terms of life and the future fun to be had with these same friends, in the next point, and in the next match.  Three, that the continuity and spirit of the contest is more important
to you than any particular point.  Even match point!

The pros know that one point matters as often as…. ummm…. Halley’s Comet!  In that case, the line judge’s
job is to take the grief anyway.  For recreational players, one point matters even less often.

Relax and enjoy your friends!

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