OC Register: Baseball’s unwritten mercy rule represents a human quirk of the information age

[AngelsWin.com]

A Vulcan and an American walked into a baseball game, bought a hot dog and a beer, and sat down side by side in the outfield bleachers. As the game got underway, the American dutifully explained the game’s basic rules. It all seemed fairly straightforward to the Vulcan – logical, even – until the first balls and strikes were called.

“Why is the strike zone changing?” the Vulcan asked.

“What do you mean?” the American replied.

“Well, that pitch was a strike the first time the pitcher threw it. It crossed home plate in the same location just now, but was called a ball,” the Vulcan said.

“Human error,” the American said, a satisfactory explanation for as long as baseball has existed.

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The longer the game went, however, a clear pattern emerged. To the Vulcan, random human error could not explain what he was seeing. The more strikes a hitter accrued, the smaller the strike zone became, reaching its smallest size when the count was 0-and-2. At 3-and-0, the strike zone was at its largest. The phenomenon was the same from batter to batter, inning to inning, pitcher to pitcher. This was more than human error. It was an expression of human compassion as each plate appearance reached its brink – something that would seem alien to, well, an alien.

Data has observed the presence of baseball’s unwritten mercy rule for years. A 2010 study published on The Hardball Times (with the appropriate title “The Compassionate Umpire”) used Pitch F/X data to quantify the changing size of the strike zone. By plotting the location of 200,000 pitches thrown to right-handed batters, the study determined that the strike zone can differ by more than a full square foot depending on the count.

Then as now, Major League Baseball has used computer-generated data points to privately audit each umpire’s strike zone for accuracy. You wouldn’t need to bring a Vulcan to a game to observe the effect: Strike zones are more uniform now than a generation ago. Strikes don’t always fall within the floating white box superimposed over home plate for television viewers, but there are generally fewer errant calls now than ever.

And yet, the mercy rule persists. If MLB’s electronic audits were intended to completely remove the human element from the strike zone, it has failed – and not because catcher framing has improved, or because random error is unavoidable. The compassionate strike zone remains alive and well in baseball’s information age.

Whether this is an intentional oversight on the league’s part, or an immutable facet of human psychology, it seems the mercy rule will exist as long as humans call balls and strikes. The pitch-tracking technology offered by Statcast, a more sophisticated successor to Pitch F/X, demonstrates how much power the count has over the strike zone in 2018.

Since umpires tend to enforce different strike zones for right-handed hitters and left-handed hitters, it’s useful to separate the two data sets. The exact probability for whether a strike is called differs slightly from count to count depending on a hitter’s handedness, but the trends are the same. There are more right-handed hitters than left-handed hitters, so the following data was culled from the larger of the two sample sizes, using Statcast’s definition of the “edge” of the strike zone.

The 0-and-0 count favors neither the pitcher nor the hitter. The at-bat is inherently closer to the beginning than the end, but the mercy rule goes into effect as soon as the second pitch is thrown. On 0-and-1, pitches thrown on the edge to right-handers that were either called a strike or a ball favored the hitter 60.8 percent of the time. On 1-and-0, the call favored the pitcher 55.1 percent of the time.

Not surprisingly, umpires became particularly empathetic on 3-and-0. Pitches taken on the edge were deemed a strike 65.4 percent of the time. On 0-and-2, umpires were even more compassionate, giving the ball on the edge to a hitter 73.8 percent of the time.

The data reveals another phenomenon more easily missed. The 1-and-1 and 2-and-2 counts are just as neutral as 0-and-0. Yet here too we see the strike zone shrinking as the count deepens. Pitches taken by right-handers on 1-and-1 favored the hitter 57.1 percent of the time, and 65.7 percent of the time on 2-and-2.

If this is truly a fixed phenomenon, we would expect hitters to respond in turn. Why not extend an at-bat whenever possible, knowing the strike zone will generally trend smaller? If analytics had a perfect grip over hitting theory, pitches per plate appearance should be trending upward.

Indeed, this appears to be the case. According to Baseball Reference, the average plate appearance hovered between 3.81 and 3.82 pitches each season from 2011-15, then spiked to 3.87 in 2016. Last year, that number rose to 3.90. With a couple weeks left in the 2018 regular season, the average plate appearance was lasting 3.91 pitches through Tuesday.

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Some of baseball’s more analytically inclined teams seem to be pushing the trend. The Philadelphia Phillies hired a new general manager prior to the 2016 season, Matt Klentak, and quickly shot up the pitches-per-plate appearance leaderboard. They rank second in MLB this season at 4.03.

The Dodgers hardly seemed intent on driving up the pitch count before Andrew Friedman was hired in 2015. Now, they are on pace to see more pitches per plate appearance (4.06) than any team this decade.

Two-tenths of a pitch might not seem like a lot, but even in a game featuring the minimum 27 plate appearances, that little bit of patience adds an extra five pitches to the length of a perfect game. Umpire compassion probably isn’t the most significant factor affecting the time of a baseball game, but it can’t be ignored.

Correlation does not equate to causation, so we should be careful not to overstate the effects of the Mercy Rule. Before trying to explain it to your Vulcan friends, it’s a good idea to buy another beer.

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