Pitch-Tracking Technology: From PITCHf/x to Hawk-Eye
How baseball learned to measure every pitch, from radar guns and QuesTec to PITCHf/x, radar-based Statcast and Hawk-Eye cameras. What the systems measure, how they work, what they changed and where they fall short.
For most of baseball's history a pitch was described by words. It was fast, it broke sharply, it was high, it was a strike. The radar gun gave one number, the speed, and even that depended on where and when the reading was taken. Today every pitch in a major-league game is measured in dozens of ways: how fast it left the hand, how much it spun and around what axis, where the ball was released, how far it moved from a straight line, and exactly where it crossed the plate. The change took about two decades and came in stages, each with its own technology.
This article follows the tools in order: the early umpire-evaluation systems, PITCHf/x, the radar-based Statcast of the middle 2010s and the camera system called Hawk-Eye that took over in 2020. It explains what is measured, how a ball's flight can be calculated from those measurements, how the data changed pitching, hitting and umpiring, and the limits that every tracking system still has. It is a description of how the systems work in general terms. Exact specifications change, and the official sources are the authority.
The physical side of the ball and its materials is covered in how a baseball is made. The effect of thin air on flight is the subject of the article on altitude and weather at Coors Field.
Before tracking: the radar gun and the scouting report
For decades the main measuring tool was the radar gun, a handheld device that measures speed using the Doppler effect: a radar signal bounces off the moving ball and returns at a slightly shifted frequency, and the shift reveals the speed. Guns were useful, but they were not consistent. A reading could depend on the type of gun, where the operator stood and at what moment the gun measured the ball. A figure from one park could differ from the same pitch measured in another. Fans and scouts spoke of velocity as though it were a fixed number, when it was often a rough one.
Everything else was judgment. Scouts described a curveball as having a "12-to-6 break" or a slider as having "late bite", and broadcasters estimated how far the ball moved. Hitters talked about the way a ball "jumped." These descriptions held real information from experienced observers, but they could not be compared across people or across years.
The first systems: umpire evaluation
The first widely used electronic tracking in major-league parks focused on the strike zone. QuesTec, a system installed in several parks in the early 2000s, used cameras to track pitches for the purpose of evaluating umpires. Umpires could be graded on their calls, and the results drew criticism, including from the umpires themselves, who questioned the accuracy and the way the data was used. The system was later replaced.
QuesTec made one thing clear. If a camera could locate a pitch relative to the strike zone, the same technology could provide data for far more than umpire grades. The next system was designed with that broader aim.
PITCHf/x: a public data set
PITCHf/x was developed by the company Sportvision and was installed in major-league parks in the late 2000s. It used cameras mounted high above the field, usually on the roof or upper deck, to follow each pitch from the pitcher's hand to the plate. From the camera images, the system computed a path for the ball and from the path derived the quantities that mattered: speed at a fixed distance from home plate, the plate location where the ball crossed, the amount of horizontal and vertical movement, and the angle of release.
Two things made PITCHf/x important. First, it was consistent: every park used the same method, so a reading in one city could be compared with one in another, apart from calibration differences. Second, the data became available to the public. Analysts and fans wrote their own programs to download and study millions of pitches, and a body of independent research grew around it. The classification of pitch types, the measurement of how much a slider breaks, the study of how pitchers sequence pitches and the evaluation of catchers by how often they turned borderline pitches into strikes, a skill now called framing, all drew on PITCHf/x data.
The system had limits that its users knew. Calibration varied from park to park and sometimes from night to night, which meant that velocity readings could be off by a small amount, and there were occasional errors in classifying pitches. Camera-based tracking also had a hard time measuring spin directly, so spin was inferred from the ball's movement and not measured. Those were the weaknesses the next generation addressed.
Statcast and radar: the 2015 expansion
In 2015, Major League Baseball introduced Statcast in every park. It combined two kinds of equipment. A Doppler radar system, supplied by TrackMan, tracked the ball from the moment it left the pitcher's hand through its flight and, on batted balls, through the air. Separate cameras tracked the movement of players, which allowed the system to measure running speed, route and throw distances. The result was a measurement of the whole play: the pitch, the swing, the batted ball and the fielders.
Radar changed the quality of the information. Because it follows the ball with a radio signal, it measures spin as well as speed. Spin rate, the number of revolutions per minute, and spin axis, the direction of the spin, became public statistics. Batted balls received two new standard measures, exit velocity and launch angle, which are explained in the article on exit velocity, launch angle and barrels. Pitchers also had their release point and the extension of the delivery measured, meaning how far in front of the rubber the ball leaves the hand.
The public could now look up figures that had been available only to clubs. At the same time, the clubs themselves had access to their own, more detailed data feeds, which they used in scouting, in player development and in game strategy.
Hawk-Eye: cameras take over in 2020
For the 2020 season, MLB moved Statcast from radar to a camera-based system supplied by Hawk-Eye Innovations. The company is known for its work in tennis and cricket, where the same technology judges whether a ball was in or out. In baseball, multiple high-speed cameras placed around each park record the ball and the players, and software reconstructs the three-dimensional positions of both. The system tracks not only the ball but also the bodies of fielders and hitters as a set of connected points, which allows measurements of the way a player moves.
The change was a shift in method rather than in the type of information. Optical tracking has advantages. It can follow many objects at once, it does not depend on a single radar line of sight, and it can produce a record of the whole field. It also has costs: it depends on lighting and on the quality of the cameras, and it calls for careful calibration. Small differences between systems are possible, which is why comparisons across the change deserve care.
What is measured: a short glossary
| Measure | What it means | Why it matters |
|---|---|---|
| Release speed | How fast the ball is moving as it leaves the hand | The basic measure of velocity, and the starting point for flight |
| Spin rate | Revolutions per minute | Affects how much the pitch moves |
| Spin axis | The direction the ball is turning | Determines the direction of the movement |
| Release point | Where the ball leaves the hand in space | Hitters see pitches that share a release point as similar |
| Extension | How close to the plate the ball is released | A pitcher with long extension gets the ball to the plate sooner |
| Movement | The difference between the actual path and a path without spin | Describes how much the ball breaks |
| Plate location | Where the ball crosses the plate | Used to judge strikes |
These measures work together. A fastball with high spin and a high release point can stay in the strike zone longer, so it appears to rise relative to what a hitter expects, even though no pitch actually rises. Hitters learn what a pitch looks like at the release point, and a pitch with a different arm slot or release can surprise them.
A worked example: why no fastball really rises
The physics of a pitch can be understood with a short calculation, using round numbers. A ball thrown at 90 miles per hour is moving at about 132 feet per second, since a mile per hour is about 1.47 feet per second. If it travels about 55 feet from release to the plate, the time of flight is roughly 55 divided by 132, or about 0.42 seconds.
Gravity pulls on the ball throughout. In 0.42 seconds, an object released with no downward velocity falls about half of gravity's 32 feet per second squared, times 0.42 squared, which is roughly 2.8 feet. That is how far a pitch would drop below its starting line if there were no spin and no air resistance. A pitcher who throws a four-seam fastball with strong backspin generates a force upward, called the Magnus force, that offsets some of that drop. The ball still falls, but it falls by less than a hitter's brain expects from a pitch of that speed. The hitter perceives a ball that "rises" relative to his prediction, when in fact it has simply dropped less than predicted.
Tracking systems make this concrete. They report the induced movement, the difference between the real path and the path that gravity alone would produce. A pitch with a large positive induced vertical movement is one with more backspin that fights gravity more effectively. This is also why two fastballs at the same speed can look completely different to a hitter. It is a calculation based on assumptions, with no air resistance, and real tracking data uses far more precise models.
What the data changed
Pitching. Pitchers and coaches can now see exactly what each pitch does and design pitches deliberately. A pitcher who wants a slider with more sweep can try grips and release changes, measure the result and keep the version that works. Training facilities use portable devices that provide the same measurements to amateurs. Pitch mix has also changed, as clubs learned which pitches perform well against which hitters.
Hitting. Exit velocity and launch angle gave hitters a target. A hitter who hits the ball hard but on the ground can see the number and try to change his swing. The data also supported the move toward hitting the ball in the air that shaped the game in the 2010s.
Defense. Fielder tracking made it possible to measure range and the first step. Defensive metrics such as Outs Above Average depend on this kind of data.
Catching and umpiring. Plate location data made catcher framing measurable, and it gave fans a way to compare an umpire's calls with the rulebook zone. Public displays of the strike zone during broadcasts made every borderline call a topic of discussion. The article on catcher's gear shows how much the position has changed in other ways.
Robot umpires and the challenge system
The most visible use of the technology is the automated ball-strike system, often called ABS. The idea is to use tracking to decide whether a pitch crossed the strike zone. Two versions have been tested in the minor leagues and in other leagues. In the first, the system calls every pitch and an umpire hears the result in an earpiece. In the second, a challenge system, a human umpire calls the pitch as usual and a hitter, a pitcher or a catcher may challenge a call, with the system serving as the final judge. The challenge version keeps the human umpire on the field and limits the number of challenges per team.
The strike zone itself is defined in the rules as the space over home plate, from the hollow beneath the batter's kneecap to the midpoint between the top of his shoulders and the top of his uniform pants. A tracking system must measure the batter's size for each plate appearance and then determine whether any part of the ball passed through that zone. In September 2025 MLB approved the challenge version for the major leagues beginning with the 2026 season, so readers should check MLB for the current rules.
Limits and cautions
No tracking system is perfect, and the numbers should be read with care.
- Measurement error. Every system has some error, which is larger for some measures than for others. Differences of one or two miles per hour or a small amount of spin should not be treated as meaningful.
- System changes. When the equipment changes, as it did in 2020, small shifts are possible, and comparisons across the change need caution.
- Context. A number describes the ball, not the situation. A fast pitch thrown in the wrong place is hit as hard as a slow one.
- Missing history. The historical record that this site uses for historical statistics has none of this data. Nothing about spin, movement or exit velocity is available for players before the tracking era. The site's leaders pages carry the traditional figures.
Even so, the improvement over the radar gun and the scout's notebook is large, and it has changed how the sport is played and discussed.
Common questions
What was PITCHf/x? A camera-based pitch-tracking system installed in major-league parks in the late 2000s that produced public data on speed, movement and location.
What replaced it? Statcast, which began in 2015 using radar, and later, from 2020, a camera-based system built by Hawk-Eye.
Can tracking measure spin? Radar and modern camera systems can measure spin directly. The earlier camera systems inferred it from the movement.
Does the data exist for old seasons? No. Historical figures like those in the historical record stop at the box score and have no pitch-level information.
Will robots replace umpires? Tracking can call the zone, and MLB approved a challenge system for the major leagues beginning in 2026, in which the human umpire still calls pitches. Check MLB for the current rules.
Where to go next
For a broader tour of the statistics built on tracking data, browse the stats and analytics topic page. For the story of one franchise across two cities and many eras of change in the game, see the history of the Los Angeles Dodgers, and for the tools that measure traditional statistics, try the stat calculator.