‘Subject To Review’ Goes Behind-The-scenes To Explain Tennis’ Hawkeye

Avid sports fans welcome historical and behind-the-scenes presentations offering unique insight into their favorite spectator sport, mine being tennis. Addressing that desire for additional knowledge, ESPN’s 30 for 30 Shorts Documentary “Subject to Review” provides a rare opportunity to learn about tennis’ instant replay, known as Hawkeye: its history, its calibration, and its limitations. 

Before explaining and exploring Hawkeye, “Subject to Review” gives historical background, beginning in 1872 with Eadweard Muybridge’s involvement in a bet wagered by Leland Stanford, founder of the university that bears his name and a race horse owner. Stanford argued that a galloping horse’s four hooves were entirely off the ground at some point in the horse’s stride, but he needed scientific evidence. In 1878, after a series of difficulties in his own life, professional landscape photographer Muybridge initiated a stop-motion experiment that won Stanford’s $25,000 wager. To provide proof, Muybridge staged twelve glass-plate cameras in a line along a backstretch. The galloping horse triggered each camera as it snapped a thread (replaced later by a clock driven device), thereby creating a convincing series of photographic images. This new stop-motion tool was quickly embraced, the first photo finish image deciding the winner of a horse race in 1881. 

After this quick introduction to the idea of a scientific answer to visual human limitation, “Subject to Review” launches into its central concern—specific details about Hawkeye. It underlines the need for such an accessory by including a sample of critical, and at times erroneous, judges’ line calls; for example, during the 2004 New York quarterfinals between Serena Williams and Jennifer Capriati, occurring before Hawkeye had received approval for tournament play. In fact, in 2004, Hawkeye, a new broadcast technology developed by a private company, was just being tested. In 2006 it received approval for tournament play. 

Using fascinating 3D footage and real people, the documentary illuminates Hawkeye’s job, explaining that it does not actually supply replay but simulation. We learn a wealth of details regarding Hawkeye and the need for the technology, even though there are eight line judges and a chair umpire in “one of the most officiated sports in the world.” As the narrator Michael Grant states, “Instant replay democratizes action on the court,” that is, decides who is right when a call is challenged by a player—the line judge or the contestant. But though ten cameras surround the court carefully calibrated for maximum coverage, and though Hawkeye shoots 150 frames per second, we’re reminded that no system is perfect but only as good as the technology. And “International Tennis Federation’s testing revealed that Hawkeye had an average error of plus or minus 3.6 millimeters.”

With fans accustomed to watching Hawkeye definitively decide disputes these days, the demonstration of the way all this works is a revelation, especially that there is “no true measurement of a ball’s position, just measurements accepted as authoritative.” As interesting, the way the Hawkeye ‘replays’ appear—with 3-D models of the arena, the correct court colors, the advertisements, the audience—adds to the convincing idea that it is 100% correct, even when it isn’t. We can’t believe our eyes—or Hawkeye’s. What this inside-the-technology explanation reveals is that our certainty in those hairline differentials can be misplaced, as impressive as the measurements are. 

My only quarrel with the documentary is the self-conscious inclusion of brief scenes with voice actor Michael Grant, footage inserted sparingly but unnecessarily in the 37-minute running time. I also find his voice too soothing for what I consider something as exciting as the world of professional tennis. But these are minor reservations for a documentary that looks behind the curtain, “Wizard of Oz” style, to reveal the truth about Hawkeye. I’ll never look at those simulations, in person at the stadium or on television broadcasts, the same way. “Subject to Review” screens and streams on ESPN from December 22.