TAMPA, Fla. — A new computerized system designed to call balls and strikes will be trialed during Major League Baseball’s spring training exhibition games, beginning this Thursday. This follows a series of tests over the last four years in the minor leagues.
Baseball Commissioner Rob Manfred supports the use of the Automated Ball-Strike System (ABS), which could be integrated to assist umpires at home plate as early as 2026, though it is not expected to replace them. For the 2024 season, the focus will shift to a challenge system, where human umpires will make the original calls, potentially paving the way for adjustments based on data from the spring trials, which may influence Triple-A games this year.
The ABS operates by equipping stadiums with cameras that monitor each pitch to determine if it crosses the plate within the defined strike zone. In the preliminary tests, umpires received audio cues via earpieces indicating “ball” or “strike” as they communicated decisions to players and fans using standard gestures.
The added complexity of the challenge system will allow each team to contest two calls per game during spring training, while initial calls will still come from human umpires. Teams will retain their challenge if it is upheld, similar to how video reviews operate in Major League Baseball, which began with home run calls in August 2008 and expanded to various calls starting in 2014.
Only the batter, pitcher, or catcher may initiate a challenge, signaling by tapping their helmet or cap, with no assistance allowed from the dugout. Challenges must be made within a 2-second timeframe, and pitch graphics will appear on scoreboards for fans to see. The average time from challenge to resolution is estimated to be around 17 seconds.
MLB has implemented this system in 13 spring training venues, which serve 19 teams. In Florida, stadiums host games for teams such as the Detroit Tigers, Minnesota Twins, New York Mets, and others, including the shared venue of Miami and St. Louis. Meanwhile, five testing sites in Arizona include joint teams, such as the Diamondbacks with the Rockies and the White Sox with the Dodgers.
Approximately 60% of spring training games will utilize this trial system, though the number of ABS games will vary per team; for instance, the Diamondbacks are set to play 29 ABS games, whereas the Cubs will only have seven.
The technology relies on a Hawk-Eye pose-tracking system, which uses cameras to analyze whether pitches fall within the boundaries of the strike zone based on each batter’s height, measured before the first test game. The equipment utilizes eight cameras at most test stadiums, with 12 installed at the Diamondbacks/Rockies venue.
While traditional MLB umpiring typically results in an oval-shaped strike zone, the ABS defines its zone as rectangular, in alignment with the official rulebook. There have been challenges in establishing an agreed-upon digital strike zone.
The MLB began experimenting with ball-strike technology during the independent Atlantic League in 2019. A test version of the challenge system was piloted in 2021 at eight venues within the Florida State League. This system transitioned to five Triple-A parks in 2022 and expanded to all Triple-A locations the following year, initially involving a mix of automated and human calls before becoming entirely challenge-based in June 2023.
Last season, teams utilizing the challenge system in Triple-A had an overall success rate of 51%. Defensive challenges had a success rate of 54%, with offensive challenges slightly lower at 48%. The average number of challenges per game was around 3.9. By comparison, major league video reviews last season had a success rate of 53.7%, with the Boston Red Sox leading at 67.9%. Challenges were more frequent later in games, suggesting a strategic shift in how teams approach this aspect of play.
Over time, MLB has revised the dimensions of the ABS strike zone. It started with a width of 19 inches in 2022 but was later reduced to 17 inches to match home plate. The height has also been adjusted: the upper limit of the strike zone was set at 51% of a player’s height in the past two years but increased to 53.5% in 2024 following feedback from pitchers. The bottom limit has consistently been established at 27%. Notably, a batter’s stance during delivery is not considered in this evaluation.
The ABS determines strike or ball decisions at the midpoint of the plate, contrasting with the rulebook’s definition, which states that any part of the ball crossing over certain zones constitutes a strike. Evidence indicates that implementing ABS could increase strikeout rates by 0.5% and walks by 1% in full ABS games compared to games without the system.
Concerns have arisen regarding how the automated strike zone might affect broadcasts and viewer engagement. To address these, MLB plans to experiment with various broadcast configurations to minimize potential bias during the challenge process.
Players will also have a means to provide feedback regarding pitches, with applications available on iPads in the dugouts. This app, named ProTABS, will allow players to compare pitches against their personalized strike zone metrics. The data will be updated after every at-bat, giving players a chance to voice their opinions on specific pitches and the overall functioning of the system.
