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How Have MLB Umpires Fared in Calling Balls and Strikes? A Look at the Data on Human vs. Robo Umpire

Umpires have one of the toughest and most scrutinized jobs in sports. Their ball and strike calls behind home plate have always been a source of controversy and debate, but the rise of pitch tracking technology over the past 15+ years has put their performance under the microscope like never before. With fans, players and analysts able to review pitch locations on TV and online after the fact, the pressure is on umpires to get more calls right.

But how have they responded to that pressure? The data shows that MLB umpires have improved their ball-strike accuracy significantly since the advent of tools like PitchFX and Statcast to grade their work. Multiple studies have found that umpires are now getting over 90% of calls correct, up from around 80% 15 years ago. The improvement has been steady almost every season as umpires get more training with the technology and feedback on areas to improve.

Younger Umpires Perform Better

Analysis by sites like Umpire Scorecards shows younger umpires perform better than older ones, which indicates potential age-related declines in vision or reaction time. Umpires in their 20s and 30s have the best accuracy, while those in their 60s grade the worst. The gap widens for pitches on the edges of the strike zone.

These results align with research by Mark Williams, a Boston University professor who has tracked umpire calls for over a decade. His data reveals umpires tend to peak in their 40s and decline in their late 50s and 60s. In 2022, his metrics ranked umpires aged 60+ as missing 17.3% of close calls compared to just 14.6% for younger umpires.

Williams believes MLB is now prioritizing bringing in better, younger umpires to continually improve performance behind the plate. Last season saw a record 10 umpires retire, and they were replaced by a "dream team" of umpires in their 30s. If the aging patterns hold, having younger umpires could drive ball-strike accuracy even higher in coming seasons before any potential decline later in their careers.

What About Robot Umpires?

Even as human umpires improve, there has been growing momentum and testing around an automated ball-strike system (ABS) using tracking technology to call every pitch. ABS made its debut in the independent Atlantic League in 2019 before expanding to all Triple-A parks in 2023.

Under the system, umpires wear an earpiece relaying ball-strike calls made by TrackMan radar, and they simply relay those calls on the field. Early results showed the automated zone slightly increased called strikes, which could negatively impact offense. But the system was very accurate, rarely missing calls compared to umpires.

To balance keeping a human element vs. maximum accuracy, Triple-A is trying out a "challenge" system this season. Teams have three challenges per game to appeal an umpire's call, with TrackMan then determining the correct call. This still leaves umpires making most calls, but gives a limited ability to overturn clear mistakes.

The improvement of MLB umpires raises some interesting questions around the need for and timing of an automated zone at the big league level. If younger umpires can keep pushing accuracy above 95% or more, would it be worth disrupting the human element and flow of the game? Some skeptics still doubt technology can call a nuanced zone adapting to context the way umpires do.

But most view automation as inevitable at some point. The question is how much nearer-perfection umpires can get before facing replacement, and whether the phase-in of a challenge system might create a transitional period. For 2023 at least, the focus will remain on human umpires reaching new heights in balls and strikes. If the trend continues, they may hold off robots a while longer and restore some faith in the men in blue behind the plate.

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