NY Times: The Strike-Zone Revolution

In his paper, Mills attributes between 25 percent and 40 percent of the scoring decline stems from the larger strike zone, and he said that he considered that estimate conservative.  The zone may have begun growing about a decade ago, when Major League Baseball began using video to evaluate umpires’ calls behind home plate. But the 2009-10 off-season, when the league put a more comprehensive system into place, seems to have been a turning point. Umpires now receive a report after each game breaking down their performance.  The result seems to be a strike zone that is both more accurate, as far as the rule book is concerned, and more consistent. A third recent analysis, by Jeff Sullivan of Fan Graphs, found that the variation in umpire calls on low pitches has declined in the last five seasons. A strike (or ball) for one umpire is more often a strike (or ball) for another.

WSJ: Scoring in Baseball Is Down. Blame the Umpires A Study Found That Umpires Have Expanded Their Strike Zone in Recent Years

The rate of correct strike calls has increased 9% from 2007 to 2013, Mills found, while the correct ball rate has increased 2.63%. According to Mills’s analysis, these shifts can account for as much as 40% in the decrease in ERA over that span. And it isn’t just that umpires are calling more strikes; they’re doing it more accurately. In particular, umpires have been calling lower strikes, by the batter’s knees. The odds of getting a hit on one of those pitches, Mills said, are 27% lower than other pitches.

Fivethirtyeight: Four Strikes And You’re Out

Hey, its Enrico Palazzo!

Consider a forgotten game in April 2010 between the Cleveland Indians and the Chicago White Sox. The White Sox were up a run with two outs in the eighth. Their set-up man, Matt Thornton, was on the mound, protecting a lead with a runner on first and the right-handed Jhonny Peralta at bat. Ahead in the count with one ball and two strikes, Thornton froze Peralta with a slider on the outside half of the plate, a couple inches below the belt. For a pitch like that, the umpire, Bruce Dreckman, would normally call a strike — 80 percent of the time, the data shows. But in two-strike counts like Peralta’s, he calls a strike less than half the time.

Sure enough, that night Dreckman called a ball. Two pitches later, Peralta lashed a double to right, scoring the runner and tying the game. Neither team scored again until the 11th, when Cleveland scored twice to win the game. Had Peralta struck out to end the top of the eighth, Chicago almost certainly would have won.1

This one call illustrates a statistical regularity: Umpires are biased. About once a game, an at-bat ends in something other than a strikeout even when a third strike should have been called. Umpires want to make the right call, but they also don’t want to make the wrong call at the wrong time. Ironically, this prompts them to make bad calls more often.