This tells part of the story:
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<b>Tennis scorers make plenty of unforced errors
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By Douglas Robson, Special for USA TODAY
July 2007
<b>What exactly is an unforced error? Who decides?</b>
As the US Open Series winds its way through North America the next six weeks, telecasters and newspapers will refer to various statistics to quantify the outcome of matches. Some will be objective numbers such as aces, double faults and break points converted.
But they will also cite unforced errors, a vast gray area of subjectivity frequently treated like science.
Separating a forced from an unforced error can depend on a combination of split-second factors such as spin, pace and player positioning. Circumstance and psychology also factor in: Is the score close or lopsided? Was a player forced to go for a winner or should he have put the ball back into play?
<b>None are easily judged in an instant, and often these numbers are gathered not by pros but by volunteers.</b>
"This is something that has driven me crazy for years," says U.S. Davis Cup captain and ESPN commentator Patrick McEnroe, who decries the "huge inconsistencies and discrepancies" in the system.
"If (Rafael) Nadal hits a forehand crosscourt high up around his opponent's shoulder and the guy misses, it's called an error," McEnroe adds. "That's asinine."
Most official statistics are gathered by the chair umpire, who enters the score and information such as first serves and second serves into a handheld device that then calculates stats such as percentage of points won on first serve. These are hard, objectively recorded and observed figures. The four Grand Slam tournaments and the ATP tour track and publicize these numbers.
Neither the men's nor the women's tour officially tracks unforced errors and other stats such as forehand winners or percentage of net approaches won. Companies such as Information & Display Systems (IDS) and IBM, which often use non-paid volunteers with their own experts, do these.
Like assists in basketball or fielding errors in baseball, what constitutes a forced or unforced error is sometimes in the eye of the beholder. One person's winner is another person's mistake.
"It's a little bit like the strike zone in baseball," explains IDS veteran Leo Levin, who is widely considered the godfather of stats for professional tennis.
"There's a written definition for it, but (that) doesn't mean it will be judged the same game to game or match to match," adds Levin, whose company provides stats for tennis (including the U.S. Open) and other sports organizations such as the PGA Tour, LPGA, NBA and NHL.
<b>Players are well aware of the inconsistencies.</b>
Informed he had committed 54 unforced errors in a loss in the Sony Ericsson Open in March, Roger Federer begged to differ. The numbers, complained the Swiss No. 1, didn't come close to capturing reality "because the statistics guys have no clue what an unforced error is," he said. "I had only about half that."
No. 4 Andy Roddick says, "It's subjective, so therefore you know certain places the stats are a little off and other places you're going to look like a superhero."
Levin says whereas NBA teams hire and train official statisticians, tennis — without a consolidated league structure — is subject to a larger degree of variance.
"Because unforced errors and certain other stats have no official place in the game, there are no standards for the statisticians and they vary from event to event based on budgets, level of training and the tennis experience of the people," Levin says.
At the Sony Ericsson Open, IDS staffed 15-18 volunteers, many of them veterans, along with their own personnel. By contrast, Wimbledon's team of stat collectors numbers about 50 and is managed by IBM. Most of the data enterers are students or recent grads who receive a small wage and have some tennis background, according to Keith Sohl, who has directed Wimbledon's data collection for IBM the last 18 years.
With strict definitions in place, Sohl is confident his stats — everything from serving speed and direction to net or baseline points won — are consistent and reliable. "We would argue that we have tried to take all subjectivity out of it," says Sohl, who says differentiating forced from unforced errors is the trickiest task. "I wouldn't say our guys never make mistakes. They might cough at the wrong time."
<b>Unlike many sports, the overall consistency of tennis stats is hindered by difference in surfaces.</b>
Rallies are long on clay, which produces more unforced errors. Grass, on the other hand, tends to elicit far fewer unforced errors because players hit more service winners and come to the net more (almost all passing shots, whether the approach is decent or not, are not considered unforced errors).
"The difference between stats in Australia and Wimbledon is mind-boggling," says Brad Gilbert, a former pro and current coach of Andy Murray. "Guy hits a 123-mph second serve in Australia and it's an unforced error. If it's a 72-mph serve at Wimbledon, it's not."
Comparing the subjectivity to basketball, Gilbert notes, "They used to say John Stockton averaged 15 assists in Utah and 10 on the road."
McEnroe, for one, has a solution: hire former players to become full-time statisticians.
"There are plenty of players out there who need jobs," he says. "You're telling me the ATP or the Slams can't hire former pros who are teaching somewhere and come over for four weeks a year?"