FEATURE
From torpedo bats to mechanized roofs, explore the modern-day engineering behind America’s favorite pastime.
Written by Sarah Alburakeh
Photo: Library of Congress
THE BLACK-AND-WHITE PHOTOGRAPHS that capture baseball’s earliest days are filled with packed grandstands, hand-stitched uniforms, and batters squinting into the sun as they launch a dinger. It’s the sport of summer evenings and unhurried time, where the ballgame unfolds at its own pace—not a pitch timer in sight.
Generations on, fans return on Opening Day to the same tune of “Take Me Out to the Ball Game,” now surrounded by the loudness and vibrance of 21st century technology. The engineering feats show up in the massive screens looming over the stands, drones capturing images over the field, and—in seven major league parks—retractable roofs shutting out extreme weather and climates.
The sport has evolved in more subtle ways, too. Updates to equipment can be seen in the newly designed barrels of the torpedo bats that shook up the 2025 season, and details as small as sliding mitts tucked into players’ back pockets are jarring to older fans of the game.
All these changes came about through the engineering mindset of problem solving, whether that was how to entice fans to come out to the ballgame in the unforgiving humidity of Texas, or finding a way to prevent broken fingers on a headfirst slide into second base. It may come as a surprise that some of the ideas have been around longer than you’d expect, but have only recently become technologically achievable—and acceptable to the humans officiating the game.
The 21st century ballpark is now a highly engineered environment, thanks to the pioneers who dared to try new things, the fed-up players looking for answers, and the engineers bringing the solutions to life.
In 1963, Stanford physicist Paul Kirkpatrick wrote in the American Journal of Physics that “the mass should be where the collision is expected to occur”—a principle now visible in the torpedo bat’s rebalanced barrel. Photo: American Journal of Physics
Swing Better, Batter
In the opening weekend of the 2025 MLB season, baseball bats broke the internet. Headlines blared that New York Yankees players had taken to the field with new bowling-pin designed bats supposedly engineered for home runs. Critics accused the team of playing the system. Fans rushed to defend them. Within days, the “torpedo bat” had become one of the most talked-about pieces of equipment in sports.
But although they were among the early adapters, the Yankees were not alone. By the time the controversy erupted, players across multiple teams had already been testing the new bat design for months in spring training. The inventor behind the redesigned barrel is Aaron “Lenny” Leanhardt, an MIT graduate and former physics professor at the University of Michigan, who said the public reaction arrived long after the engineering work was already well underway.
Leanhardt pivoted to coaching college baseball, then became a hitting coach first for the New York Yankees, and now field coordinator for the Miami Marlins. The shift led him to apply his physics background to one of the most traditional pieces of equipment in baseball.
“We were looking at all possible ways that we can make hitters better within the rules,” he said, noting how pitchers had found ways to generate unprecedented movement on their pitches—including illegal use of sticky substances on their fingers—presenting coaches and players with new challenges.
“If you look at how golf clubs and tennis rackets have evolved over the years, they've all gone in the direction of becoming more hitter-friendly. So that's really what this was all about—just giving the batter a larger sweet spot to work with.”
—Aaron “Lenny” Leanhardt, Field Coordinator for the Miami Marlins
The original idea was straightforward: make the bat bigger where hitters are trying to make contact. Simply increasing the size of the bat wasn’t an option, since that would also increase its weight. Instead, the solution was to rearrange the existing mass, redistributing it so the fattest part of the barrel was concentrated in the area where players are trying to hit the ball.
What ball players refer to as the “sweet spot,” physicists describe in more technical terms of vibrational modes, nodes, and antinodes. Essentially, the concepts are the same, Leanhardt explained. If a bat is struck near the tip, it vibrates strongly and transfers little energy to the ball. Move slightly down the barrel, however, and the vibrations drop dramatically. At this location, energy transfer is maximized, and the ball leaves the bat at high speed.
“It’s this magic place where the bat doesn’t vibrate, and the ball just takes off like a missile. So why don’t we make that as fat as possible?” he said, describing the premise of the torpedo bat’s design.
Transforming the idea into a usable bat was a process. Batters can’t simply switch bats without altering their swing mechanics. “The players provide the real constraints of the problem,” Leanhardt said. “They’re happy with their current bat and current swing, so how can we change the bat and still fit the old swing? A lot of modeling went into that.”
The goal of making the bat feel the same to the player while performing differently may seem counterintuitive, but in Leanhardt’s mind, it was just a pure math, physics, and engineering problem. The handle and knob needed to remain familiar. The overall weight had to stay within a narrow range. Only the distribution of that weight could change.
“Fundamentally, the goal is to have the mechanical properties of the bat be virtually identical. When he mechanically moves his body to create this swing, the bat is an integral part of that,” he explained. “And if you add more weight to the end of the bat or toward the hands, it’s going to feel different and modify their swing.”
So, part of the initial goal was to make it not feel any different at all—just play differently.
“I made a bunch of measurements very carefully of what the shape was for that region of the bat and then designed the taper as it goes from the skinny part of the handle to the fat part,” he explained. If the taper went too thin too soon, the bat would break more easily. Too thick, and the weight balance would be suboptimal. “It’s this combination of tradeoffs.”
Production turnaround was a limiting factor. “We did this dry run where we ordered a bunch of bats and then us hitting coaches just stood in there and the machine threw 99 mile per hour fastballs,” he said. “We tried our best to hit them and just broke as many of these bats on purpose as we could to make sure that they would survive a standard practice session from an actual good player trying to hit with them.
“You can call that the zeroth order iteration,” he added.
The red-shaded area in the graphic illustrates the exit velocity and launch angle combinations that yield “barreled” status in 100 percent of cases. Photo: MLB.com Glossary
Paul Goldschmidt #48 of the New York Yankees at bat with a torpedo bat against the Milwaukee Brewers at Yankee Stadium on March 27, 2025 in New York City.
Photo by Mike Stobe/Getty Images
Cal Raleigh #29 of the Seattle Mariners stands with a "torpedo bat" during the eighth inning against the Texas Rangers at T-Mobile Park on April 11, 2025 in Seattle.
Photo: Steph Chambers/Getty
Because natural wood introduces unavoidable variability, even bats made to the same specifications differ slightly in mass distribution. By measuring the period of each bat and calculating its moment of inertia using a “pendulum scale,” the coaches could select the units that most closely matched a player’s target swing weight.
“We might have ordered three different models, and within each model six different bats. Then we’d cherry pick the one most identical to what the player wanted,” Leanhardt said. Players would test the handful of versions and select the one that felt best, creating a feedback loop between engineering and athlete experience.
Leanhardt found that the players who were early adopters—those willing to experiment before the design gained public attention—were already highly attuned to their swing mechanics, and often the most precise in their feedback, making the engineering process more productive.
“I can’t guarantee that any one of those designs was truly the best,” Leanhardt said. “But I guarantee whichever one the player picked was definitely the best one.”
As a result, the first bats placed in players’ hands were already close to final performance specifications, limiting the number of design iterations required.
The whole process took about a month to go from calling up the first manufacturer to taking it into the first Major League Baseball game, according to Leanhardt.
“My first spring training with the Marlins was before torpedo bats became a big popular thing in the public, and a lot of the players were already asking about it and testing it out,” Leanhardt said. “We got some bats ordered for the guys last year during spring training. A couple of them used it all season and had a lot of success with it. There’s definitely guys swinging it on all the teams at this point, in all the organizations.”
SLIDING MITTS
The sliding mitt traces back to 2003, when former major leaguer Scott Podsednik—one of the game’s fastest baserunners and a 309-career stolen base threat—began wearing a hard plastic thumb guard after an injury sustained during headfirst slides.
In 2008, after breaking his pinkie sliding into second, he worked with a hand therapist to develop a custom protective cast shielding all five fingers: a crude but effective prototype. By 2009, he was sliding into second base with what looked like a padded batting glove wrapped in black tape to match his Chicago White Sox uniform.
By 2013, other players took notice, and similar mitts were appearing across Major League Baseball. What Podsednik once described as a personal fix was spreading. “I had no idea it would turn into what it has,” he later said of the now popular accessory.
Today, the jokingly nicknamed “oven mitt” has become both protective gear and cultural accessory. Stars like Aaron Judge and Bryce Harper sport custom designs, while youth players wear them as style statements to emulate their big league favorites (even where headfirst slides aren’t allowed).
Modern versions rely on strategic stiffness: rigid thermoplastic or carbon-fiber inserts shield fingers from axial and torsional loads, while flexible compression fabrics preserve dexterity, concentrating protection where impact occurs and compliance where motion is required.
Photo: Getty
Fields of the Future
Once upon the 1800s, baseball was played in wooden ballparks (eventually deemed fire hazards), followed by the concrete and steel “jewel box” stadiums of the early 20th century. The growth of the sport’s popularity and its spread beyond the northeastern states led venues to transform into the multipurpose modern facilities we know today. They now needed to accommodate more fans—and tolerate harsher climates.
Unlike other sports, baseball allows wide variation in its stadiums beyond the infield, resulting in ballparks with dramatically different field dimensions. Most ballparks did share a defining trait, though: they were open to the elements. In more extreme climates, that exposure can make or break the experience. Arlington Stadium, the longtime home of the Texas Rangers, was widely regarded as the hottest stadium in Major League Baseball for much of its existence. Gametime temperatures frequently climbed well into triple digits, with fans and players alike enduring the sun beating down on their necks.
There may be no starker contrast to that experience than its replacement, Globe Life Field.
The $1.2-billion, 40,500-seat venue can transition from an open-air ballpark to a fully enclosed, air-conditioned facility in approximately 12 minutes. At its center is a six-acre retractable roof—the largest single-panel operable roof in the world—designed to shield fans from extreme heat, prevent rain delays, and open on cooler evenings for outdoor games under the stars.
Retractable roofs move in different ways. The dual rail system of the Miami Marlins’ flat stadium roof is an example of traction drive. At Globe Life Field, the retractable roof does not slide in sections or panels. It moves as a single, unified structure.
Each 35-foot-long, 120,000-pound roof bogie rides on six wheels. To prevent misalignment damage, engineers built what Agosto calls a “spring fuse,” preloading each wheel so “all six wheels stayed in line and true,” permitting movement only when forces exceed a preset threshold. Photo: Uni-Systems Engineering, PC
Early construction on Globe Life Field. Photo: Uni-Systems Engineering, PC
Andrew Agosto, vice president at Uni-Systems Engineering, served as the engineer of record for the roof’s mechanization system, overseeing its design, supply, installation, and testing. Trained as a structural engineer himself, Agosto coordinated with the ballpark engineers to integrate the moving roof between the stadium bowl and the long-span structural steel above it.
“When you take a structure and you start moving it, that changes things. Little things become big things, and stiffness becomes a very important factor as soon as you start moving something heavy,” he said.
The roof weighs roughly 24 million pounds, explained Agosto, and is supported by 10 steel trusses spanning approximately 620 feet between rails on the north and south sides of the stadium. When in motion, the roof travels more than 400 feet along those rails, carried by 20 massive bogies that must remain precisely aligned over the full length of travel.
“This thing is all one piece moving together and managing that weight was a big challenge,” Agosto said. "Alignment is always a big factor, but it’s much more important over that distance because you don’t have the relief of separate panels.”
As a solution, Uni-Systems incorporated multiple layers of release and compliance into the roof’s design. At a global level, the system allows controlled movement between the roof structure and the supporting bowl to accommodate wind loads, thermal expansion, and construction tolerances. “The tolerancing over the length of the construction of both the rail and the structure itself led us to some of the new technology we put into this one,” Agosto said. “This was the first roof we did that had lateral release systems within a single bogie.”
Uni-Systems also worked on the retractable roof of Daikin Park (formerly Minute Maid Park, home to the Houston Astros) and LoanDepot Park (the Miami Marlins’ home). And while RFK Stadium in Washington, D.C., didn't see the need for a retractable roof, it does notably have a retractable pitcher’s mound to easily convert the ballpark into a soccer field—a serious retrofitting potential for other stadiums currently hosting their local FC in less optimal settings.
Designing for motion means accounting for inertia and braking loads—conditions that static structures never experience.
“Whenever you start moving something, now you have all your inertia loads, right? You’ve got to take into account your accelerations,” Agosto said. While variable-frequency drives allow the roof to start and stop smoothly under normal conditions, the system is also designed to withstand abrupt emergency stops.
“If you can imagine, you’re traveling at nearly 40 feet per minute, which is roughly a fast walking pace, and then you just stop on essentially a few inches worth of stopping distance of a 24-million-pound roof… it shakes the whole building,” he explained.
Energy-absorbing end stops and redundant control systems provide additional protection, ensuring the roof can be safely halted even under worst-case scenarios.
The bogie level is where some of the biggest longevity improvements came. Each of the 20 bogies, roughly 35 feet long and weighing about 120,000 pounds, carries six wheels. In previous designs, Agosto said, those wheels had no compliance. Even slight misalignment across that span could generate significant forces in the bearings and wheel flanges, increasing loads and accelerating wear.
To address that, engineers fitted all 120 wheels with lateral springs perpendicular to the direction of travel, creating what Agosto described as a “spring fuse.” Each spring is preloaded to hold the wheels firmly in place under normal operation, only allowing movement when forces exceed a preset threshold, such as during misalignment or obstruction.
The built-in compliance absorbs abnormal loads before they can damage the bearings—a change Agosto said should significantly extend bearing life compared with previous stadium roofs, where bearings required periodic replacement.
Photo: Uni-Systems Engineering
“A big factor in this one was just the sheer size. From a weight standpoint, this was roughly 24 million pounds total, which isn't necessarily the heaviest, but it is the biggest single-panel retractable roof. The only thing that comes close is the enclosure at Chernobyl.”
—Andrew Agosto, Vice President at Uni-Systems Engineering
Critical Cooling Comfort
Once the roof is closed, Globe Life Field functions as a fully indoor stadium—but the mechanical work is only half solved. From there comes the task of keeping the place cool and comfortable, which, in a venue of that size, puts extraordinary demand on its mechanical systems.
Lauren Berry, P.E., LEED AP at ME Engineers, was the lead mechanical engineer on the project, overseeing the design of the stadium’s HVAC systems from concept through post-construction. For Berry and her team, the challenge was not simply cooling a massive volume of space but doing so intelligently in a scorching climate.
“An indoor baseball stadium in Texas is so much more critical than it would be to do an indoor baseball park in Chicago,” Berry said. “They’re playing the entire season during the extreme temps.”
Rather than attempting to maintain a uniform temperature throughout the entire seating bowl, the system intentionally leverages thermal stratification. Air distribution is split between high-bowl and low-bowl systems, focusing cooling where occupants are seated while allowing warmer air to rise toward the roof structure.
Berry emphasized that the entire bowl is still conditioned, but strategically. “We’re not keeping the temperature in that entire volume at 75 °F,” she said. “We are actually allowing massive amounts of stratification.”
Photo: Uni-Systems Engineering
A ballpark control room. Photo: Uni-Systems Engineering, PC
The result is a noticeable temperature gradient between seating levels, with differences of several degrees depending on elevation, while the upper volume near the roof is allowed to run significantly warmer. This approach reduces energy demand while maintaining comfort for fans and players.
The mechanical design was further shaped by the stadium’s transparent ethylene tetrafluoroethylene (ETFE) roof panels and extensive glazing throughout the concourses—features that introduce higher solar heat gain than solid roofing systems, increasing cooling loads within the bowl.
To compensate, the mechanical team optimized the central plant using large-capacity chillers arranged in a series counterflow configuration, extracting maximum efficiency from otherwise conventional equipment.
Beyond temperature control, Globe Life Field’s mechanical systems play a critical role in acoustics and life safety. To manage sound levels within the seating bowl, ductwork was acoustically lined—an uncommon choice in hot, humid climates, Berry explained, but one deemed necessary to meet performance goals.
Smoke control presented an even greater challenge. “Life-safety smoke control systems on this project were the most complicated many of our engineers have seen,” Berry said. Much of that complexity stemmed from the depth of the stadium below grade and the concentration of premium spaces that required protected egress routes—systems that fans rarely notice, but that play a critical role in preserving safety.
Umpires Go High-Tech
Decades ago, baseball’s own “mechanized man,” Raymond “Hap” Dumont, imagined a futuristic “magic eye” calling balls and strikes. Today’s Automated Ball Strike (ABS) system makes the tech pioneer’s vision a reality, but not through the light beams he imagined (or magic, for that matter). After years of minor league testing and spring training trials, Major League Baseball announced that ABS will debut in the regular season in 2026.
The system relies on high-speed optical tracking cameras, real-time 3D pitch modeling, and digital infrastructure embedded directly into ballparks. Developed by Hawk-Eye Innovations, ABS uses a network of synchronized cameras positioned around the stadium to track the baseball’s trajectory in three dimensions and map it against a digitally defined strike zone calibrated to each batter’s stance.
Pushback against the technology hasn’t only been about distrust or resistance to change. There’s something to be said for the human experience of error (imagine how the excitement levels would plunge without the threat of an entire dugout pouring onto the field to argue with the umpire). Doubtful fans will be relieved to learn that ABS is launching as a challenge system, not a fully automated replacement for the homeplate umpire, who still makes the live call on every pitch.
Each team is allotted two challenges per game and retains a challenge if it is successful. And if a two-challenge system sounds familiar, it’s because MLB has used replay challenges for fielding calls for over a decade. Pitching challenges, however, have so far been limited to testing environments—and only the batter, pitcher, or catcher may challenge a call by tapping their helmet or hat immediately, without assistance from the dugout.
The same tracking technology is also redefining how teams prep, coach, and evaluate players. Radar-based systems once measured ball flight; multi-camera optical tracking now captures full-body motion. High-speed cameras and AI-powered markerless motion capture let teams reconstruct joint angles, release points, bat paths, and defensive positioning in three dimensions, both in game settings and controlled training environments, according to Hawk-Eye's website.
Earlier systems could measure outcomes like velocity, spin rate, and launch angle, but optical tracking answers the “how.” Biomechanical models track joint location and bone segment orientation throughout a delivery or swing, turning what was once qualitative language into measurable kinematic patterns. Naturally, coaches are becoming increasingly data-literate—though arguably they have been since Moneyball—combining traditional instruction with analytic insights.
Photo: Getty
Photo: MLB.com
HOW ABS WORKS (IN 6 STEPS)
1. Pitch is thrown.
A stadium-mounted multi-camera tracking system powered by Hawk-Eye Innovations captures the ball’s position in three dimensions.
2. Ball trajectory is reconstructed.
Software merges the synchronized camera feeds to reconstruct the pitch’s full 3D path from release point to the catcher’s glove.
3. Strike zone is digitally defined.
Each batter’s strike zone is calibrated based on their height and stance, according to rulebook parameters.
4. ABS computes ball or strike.
For every pitch, the system determines whether the reconstructed trajectory intersects the digital strike zone, even without challenge.
5. A challenge is initiated.
Each team is allotted two challenges per game and retains a challenge if it is successful. Only the batter, pitcher, or catcher may challenge.
6. Result is displayed and enforced.
The precomputed ABS result is transmitted through broadcast and scoreboard, and the umpire enforces the updated call if needed.
Aaron Judge #99 of the New York Yankees hits a single in the fifth inning against the Toronto Blue Jays during a Grapefruit League spring training game at TD Ballpark on February 24, 2026.
Photo by Julio Aguilar/Getty Images
Fans, of course, have opinions. When a lineup reflects matchup probabilities that contradict the collective gut instinct, the backlash is swift. And yet, 2025 was a major high point for baseball viewership. Debate, after all, is part of baseball’s tradition, and what feels disruptive one season often becomes standard in the next.
The game continues to thrive through all its growing pains. A version of the ABS was imagined 75 years before it entered a major league park. A physicist outlined the logic of a rebalanced bat more than 60 years before another physicist brought the torpedo bat to life. And beyond baseball, golf clubs, tennis rackets, and football helmets have all evolved to become more forgiving and better aligned with how athletes actually make contact, generate force, and manage injury.
In that sense, Leanhardt said, his torpedo bat invention is simply part of the same progression toward more hitter-friendly design. When asked what he’ll be coming up with next, he laughed: “People like to ask that one.” Coaches and athletes may be cooking up new ideas to refine designs, he said, but only a small number ultimately reach the field.
Innovation in sports engineering rarely appears all at once. It surfaces through experimentation spurred by the needs of the game. And as history has proven time and again, the ideas arrive early; the acceptance comes later. Eventually, technology catches up, and the ballgame adjusts.
Sarah Alburakeh is strategic content editor.
© 2026 The American Society of Mechanical Engineers. All rights reserved.