Strike 3! You’re Out?

The baseball slams into the catcher’s glove. The umpire calls a third strike and yells, “You’re out!” In the past, the batter would have no choice but to trudge back to the dugout. Not anymore.

Instead, he taps his helmet, signaling a challenge of the umpire’s call. Within seconds, a digital strike zone flashes onto the huge stadium scoreboard, and an animation traces the path of the pitch in slow motion. The replay shows the ball missing the strike zone by a fraction of an inch. The umpire announces that the call has been overturned, and the at bat continues after taking 10 seconds out of the game for the challenge. On the very next pitch, the batter swings and crushes the ball for a home run! What could have been an inning-ending third out has turned into runs on the scoreboard—all thanks to the Automated Ball-Strike (ABS) system in Major League Baseball (MLB), which was adopted this season.

The baseball slams into the catcher’s glove. The umpire calls a third strike. “You’re out!” he yells. In the past, the batter would have no choice but to return to the dugout. Not anymore.

Instead, he taps his helmet. That means he’s challenging the umpire’s call. Within seconds, a rectangle flashes onto the stadium scoreboard. It represents the strike zone. An animation traces the path of the pitch in slow motion. It shows the ball missing the strike zone by a fraction of an inch! The umpire announces that the call has been overturned. The batter gets to stay at the plate. On the very next pitch, he swings and hits a home run!

The “out” call would have ended the inning. Instead, there are runs on the scoreboard. It’s all thanks to the new Automated Ball-Strike (ABS) system. Major League Baseball (MLB) adopted it this season.

The system allows players to challenge a pitch if they think the umpire made the wrong ball-or-strike call (see “How ABS Challenges Work,” below). “Hitting a baseball is the hardest thing to do in pro sports,” says physicist Daniel Russell, who studies the science of baseball hitting at Pennsylvania State University. “You’ve got a very small, very fast object. You have to hit it at just the right place and time.”

Even the best hitters in MLB get a hit in only about 3 out of every 10 at bats, says Russell. With so little time to react and such low odds of success, accurate calls matter.

Umpires call if each pitch is a ball or strike. The system allows players to challenge a pitch if they think the umpire got it wrong (see “How ABS Challenges Work,” below). “Hitting a baseball is the hardest thing to do in pro sports,” says physicist Daniel Russell. He studies the science of baseball at Pennsylvania State University. “You’ve got a very small, very fast object. You have to hit it at just the right place and time.”

Even the best hitters in MLB don’t hit the ball most of the time, says Russell. It happens only about 3 out of every 10 times they’re at the plate. Batters have very little time to react to a pitch. With such low odds of success, accurate calls matter, Russell says.

The strike zone is an invisible box centered over home plate. It measures 17 inches wide and about 24 inches high, and it is positioned between the batter’s knees and chest, directly above home plate. Throwing a ball from the pitcher’s mound, which is more than 60 feet away, is incredibly difficult. To do so, pitchers generate force using nearly their entire body. “It’s all about transferring energy,” says Brian Cammarota, an athletic trainer and physical therapist who works with baseball pitchers. “Pitchers create force in the lower body and transfer that energy to the arm.”

That energy starts in the legs. Pitchers push off the mound using their back leg while stepping forward with the front leg. Their hips and core rotate before the shoulder, arm, wrist, and fingers whip forward to release the ball. Trainers call this sequence a player’s kinetic chain. If one part of the chain breaks down, hurlers can lose speed, accuracy, and control. That often means fewer strikeouts.

The strike zone is an invisible box centered over home plate. It measures 17 inches wide and about 24 inches high. It extends between the batter’s knees and chest, directly above home plate.

The pitcher’s mound is more than 60 feet away. Throwing a ball that far is incredibly difficult. To do so, pitchers generate force using nearly their entire body. “It’s all about transferring energy,” says Brian Cammarota. He’s an athletic trainer and physical therapist who works with pitchers. “Pitchers create force in the lower body and transfer that energy to the arm,” he explains.

It starts in the legs. Pitchers push off the mound using their back leg. They step forward with the front leg. Their hips and torso rotate. Then the shoulder, arm, wrist, and fingers snap forward to release the ball. Trainers call this sequence a player’s “kinetic chain.” If one part of the chain breaks down, pitchers can lose speed and control. That often means fewer strikeouts.

A pitch can reach speeds of more than 100 miles per hour and miss the strike zone by less than the width of a fingernail. Even the best human umpires can struggle to judge every pitch’s location perfectly.

That’s why MLB built ABS. The system uses Hawk-Eye, a network of 12 high-speed cameras perched around the stadium. Each camera tracks the ball from a different angle, hundreds of times every second. A computer combines the different views and pinpoints the ball’s exact 3-D location. It then checks the ball against the strike zone. If the ball passes through the virtual box, it’s a strike. Teams get two challenges per game. If a challenge is successful, they keep it. But they lose it if the challenge fails.

Pitches can reach speeds of more than 100 miles per hour. They might miss the strike zone by less than the width of a fingernail. Even the best umpires can’t judge every pitch perfectly.

That’s why MLB built ABS. The system uses a network of 12 high-speed cameras. They’re placed around the stadium. Each camera tracks the ball from a different angle, hundreds of times every second. A computer combines the different views to pinpoint the ball’s exact location. It then checks that against the strike zone. If the ball passes through the virtual box, it’s a strike.

Each team gets two challenges per game. If a challenge is successful, they keep it. But they lose it if the challenge fails.

“Every pitch matters,” says Stuart Cheshire, a technical project manager who works on ABS for MLB. “Making the right call is fundamental to the game, and we have to get it right.”

So far, results of the system show that human umpires accurately judge most pitches. But when a call is overturned, it can change the course of a game—as it has many times this season. There’s another benefit of ABS: fewer arguments between umpires, players, and managers! With every pitch in October carrying huge pressure, MLB hopes the ABS system helps make sure the biggest games in baseball are decided by skill—not missed calls.

“Every pitch matters,” says Stuart Cheshire. He’s a technical project manager who works on ABS. “Making the right call is fundamental to the game, and we have to get it right.”

So far, ABS has shown that umpires accurately judge most pitches. But when a call is overturned, it can change the course of a game. That’s already happened many times this season. ABS also reduces arguments between umpires, players, and managers.

The MLB playoffs are happening in October. Every pitch carries huge pressure. MLB hopes the ABS system means that the biggest games in baseball are decided by skill—not missed calls.