Calling out the umpires

If you're a baseball fan, you've no doubt told yourself a time or two that you could do a better job than the home-plate umpire, but can a computer? Sports-technology company QuesTec Inc (www.questec.com) has developed a system that is already giving umpires a run for their money. In 2001, the company entered a five-year agreement with Major League Baseball to install, operate, and maintain its UIS (Umpire Information System) in every Major League ballpark. Today, the system has found a home in 13 parks. By next season, it could be in all of them. The company maintains that it does not intend for the technology to replace umpires but rather to help them improve their performance. Major League Baseball hopes that the system will also aid its effort to standardize and tighten the size of the strike zone, which in recent years has shifted lower and further outside home plate. The UIS is a more accurate and advanced version of QuesTec's PitchTrax system, which you may recognize from Fox baseball broadcasts.

QuesTec's measurement system relies on image processing, photogrammetry, and physics (Reference 1). Photogrammetry uses electronic imagery to determine an object's location without touching the object. Thus, the QuesTec system works wirelessly and requires no modifications to the ball, field, or any other part of the game.

The art of pitching and the laws of physics complicate the trajectory of the baseball (see sidebar "The physics of baseball"). Therefore, the UIS uses stereoptic viewing, appropriate algorithms, and high-speed computations to determine the path of the ball as it travels from pitcher to catcher. The system employs several stationary, high-speed, digital cameras mounted in the stands along the first- and third-base lines of the ballpark, some at field-level and some higher in the stands (Figure 1). The system at Network Associates Coliseum in Oakland, CA, for example, uses four cameras—two near the dugouts and two attached to the stadium's middle deck. The cameras are mounted off-center, so that the umpire, catcher, and batter do not obstruct their view (Reference 2). The cameras view the movement of the ball from the pitcher's hand to home plate. Computer software differentiates the ball from other moving objects in the same field of view, such as birds or windswept trash, and analyzes 12 to 16 sequential video images to precisely determine the ball's location—that is, its x, y, and z coordinates—during its flight. This data enables the system to calculate the ball's position relative to the "strike zone" projected above home plate.

But the QuesTec system doesn't entirely do away with humans. An operator watches over every system throughout the game, ensuring that the camera views remain obstruction-free and inputting information about the circumstances surrounding every pitch, such as whether a batter swings at it and what the umpire's call is. The operator, who requires no further technical knowledge than computer literacy, is stationed in a booth containing three monitors: One monitor records the game; another displays images from various cameras, alerting the operator if one of these views becomes obstructed; the third reveals the results of the ball-tracking device, including details of every pitch's speed, location, and break along the path. The system costs $30,000 to install in a park and $200 per game to operate.

The QuesTec system doesn't know whether a pitch is a ball or a strike until after the game. It uses the fixed dimensions of home plate to determine whether a pitch is inside or outside, but determining whether a ball high or low is a bit more involved and requires the operator to supply the system with some crucial information. At the end of the game, the operator uses images of each batter in his stance—taken when the first pitch to each batter is approximately halfway to home plate—to assist the system in determining individual strike zones. With a few mouse clicks, the operator manually sets electronic lines indicating the bottom and the middle of the strike zone at the hollow of the batter's back knee and belt, respectively. The system then automatically calculates the top of the strike zone, marking a third electronic line at a distance of two-and-half baseballs above the batter's belt. The system calls any ball a strike if the ball passes over the plate within these vertical limits, and if the batter doesn't swing at it or hit it or the catcher doesn't drop it.

Major League Baseball's rule book states that the strike zone is the area over home plate extending from the hollow beneath the knee to "the midpoint between the top of the shoulders and the top of the uniform pants." However, by automating the placement of the top line, the system minimizes operator influence over the vertical dimensions of the strike zone. The operator can objectively mark the belt and the kneecap but needs not make a judgment call about the midpoint between the batter's shoulders and waist (Reference 3).

The system records images and details for each pitch, including images of the player's stance and swing; the system plots the ball's path within a coordinate system as it passes over home plate and through the vertical strike zone that the system has calculated (Figure 2). All of this information is burned onto a CD-ROM, which the game's umpire receives following each game. (A copy of the CD-ROM goes to the umpire's supervisors, and another goes to the commissioner's office.) The umpire uses the CD-ROM to then review his calls and how they match up with the system's. According to QuesTec, the system is accurate to within 0.5 in. If man and machine disagree on at least 90% of the calls, the umpire's ability becomes suspect.

The system is not without its faults, however. For one thing, despite the efforts of the operator, it is not always possible to keep the system's cameras obstruction-free. For example, base coaches and players in the on-deck circle sometimes get in the way (Reference 4). Also, despite the company's calibration efforts, players and umpires alike lack confidence in the system's ability to comprehend the variations that come into play from stadium to stadium and even in the same at-bat—when a batter's stance changes in preparation for a bunt, for example. And the operator will occasionally notice that the system has made a glaring error. The system is not yet capable of correcting such errors; in the meantime, questionable at-bats simply disappear from the game record.