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"dalek" writes:

What do Don Denkinger [wikipedia.org] and Jim Joyce [wikipedia.org] have in common? If you're a baseball fan, you might recognize them as umpires who are known for famously missing a critical call late in a game on national TV. Before Major League Baseball (MLB) embraced video-assisted replay (VAR), which it resisted long after other sports like football had demonstrated that replaces could be used successfully, there was no way to reverse the missed calls. Even after MLB finally allowed VAR to be used, by far the most frequent call in a game still cannot be reviewed: whether a pitch is a ball or strike.

The technology to track the fight of a baseball and reliably determine balls and strikes has been in use for a couple of decades. Systems like QuesTec [wikipedia.org], PITCHf/x [fangraphs.com], and Statcast [mlb.com] can accurately track the flight of a baseball and determine whether its trajectory crossed the strike zone when it reached home plate. Statcast not only determines each pitch's horizontal and vertical location when it crossed the plate, but a plethora of other data [mlb.com] like the pitcher's release point in three dimensions, the velocity when the pitch left the pitcher's hand, it's spin axis and rate, the pitch's acceleration in three dimensions, and a classification of the pitch type. Despite the capability to accurately call balls and strikes automatically, MLB still relies solely on human umpires this call.

The horizontal location of the strike zone is identical for every pitch, requiring that some portion of the baseball pass above home plate. However, the vertical location [mlb.com] is defined as being from the bottom of the hitter's kneecap to the midpoint between the top of the hitter's pants and the hitter's shoulders. This is affected by the hitter's height, body shape, and their batting stance. A hitter won't have exactly the same batting stance on any two pitches, so the actual strike zone varies slightly from pitch to pitch, even for the same hitter. This data is determined by Statcast while the pitch is in flight, and is recorded in the sz_bot (bottom of the strike zone in feet above ground) and sz_top (the top, with the same units) fields in Statcast data. The flight of the baseball is currently tracked by 12 Hawk-Eye cameras stationed throughout each stadium, five of which operate at 300 frames per second. The images from the different cameras can be used to pinpoint the location of the baseball within a few millimeters [espn.com]. The same type of camera is used for VAR in tennis matches to determine if a ball was out of bounds.

When Don Denkinger mistakenly called Jorge Orta safe at first base in the ninth inning of game 6 of the 1985 World Series, known in St. Louis simply as "The Call" [wikipedia.org], it was followed by a series of poor plays by the by the Cardinals that led them to blowing a 1-0 lead and losing the game. Although the Cardinals proceeded to get blown out 11-0 in game 7, but Denkinger is often blamed for the Cardinals losing the series. Following the blown call, two St. Louis radio personalities doxxed Denkinger, who received hate mail and even death threats from irate fans. At the time, Cardinals manager Whitey Herzog was furious at Denkinger. After the series was over, Herzog became very dismayed by the harassment Denkinger received from St. Louis. It was so severe that Herzog made public appearances with Denkinger [scoopswithdannymac.com] to raise money for charity and try to get Cardinal fans to forgive the umpire.

Jim Joyce was also known for a missed force out at first base, this time what should have been the last out of a perfect game for Armando Galarraga, an otherwise mediocre pitcher attempting to complete one of the rarest feats in all of baseball. The first base umpire generally watches to see whether the fielder's foot is on the first base and when the runner's foot touches the base, listening for the sound of the ball popping into the fielder's glove. It's an extremely difficult call that umpires get correct a remarkably high percentage of the time. In this case, Joyce believed that the runner, Jason Donald, reached the base before the baseball arrived in the fielder's glove, and he called the runner safe [espn.com]. Galarraga retired the next hitter, but there was no way after the game to correct the blown call. After seeing a replay, Joyce held a press conference in which he tearfully admitted publicly that he blew the call and felt awful for costing Galarraga the perfect game.

Had MLB made use of the available technology, neither Denkinger nor Joyce would be remember for missing calls. It's possible the Cardinals might have imploded and lost the World Series anyway. In the case of Joyce, the play would have been reviewed for a minute or two, the umpire would have raised his fist to signal an out, and the Detroit Tigers players and coaches would have run onto the field after a brief awkward pause to celebrate the perfect game. Denkinger and Joyce were excellent umpires who were well-respected by players and managers but are both mostly known for making a single bad call that could have easily been corrected with the proper VAR tools.

Despite the potential for technology to further assist umpires in getting calls correct, there is significant resistance to automatic balls and strikes. While the ball-tracking technology is widely accepted by tennis fans, there are concerns that baseball fans might see pitches that appear to be balls get called as strikes, and that the technology would be viewed as untrustworthy [espn.com]. Part of the issue is that the strike zone is actually a three-dimensional volume that is 17 inches wide and 17 inches deep. If the flight of the ball intersects any part of the zone, it's a strike. For pitches with a high rate of forward spin and a lot of vertical break, it could clip the bottom part of the zone at the front of home plate, be caught well below the batter's knees, and still get called a strike.

Some fans are also reluctant to end the skill of pitch framing, in which a catcher receives a pitch that's a ball but catches it in a manner to give the illusion of it being a strike. The umpire is fooled into calling the pitch a strike anyway, giving an advantage to the pitcher. One estimate suggests that the best catchers were at one time able to save as many as 40 runs during a season with pitch framing [espn.com], which is worth roughly about four wins to the team. Some baseball purists have opposed using cameras to automatically call balls and strikes because it would put an end to pitch framing [fangraphs.com].

Instead of fully embracing robot umps to call balls and strikes, MLB intends to test a system of challenging balls and strikes at AAA this season, which is the highest level of minor league baseball. Teams will receive a certain number of challenges each game, where a ball or strike call can be reviewed and, if necessary, overturned. Part of the issue with fully embracing automatic balls and strikes is the need to determine how to set the "correct" strike zone. One option is to estimate it from the batter's height. The other is to determine in on every pitch based on the batter's stance, using the sz_top and sz_bot fields in Statcast data. If the strike zone was determined by the batter's stance on every pitch, a batter could use an exaggerated stance to make the strike zone artificially small, making it difficult to throw strikes. Although catchers would no longer be able to steal strikes with pitch framing, adjusting the strike zone for every pitch could allow hitters to steal balls.

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