The Playoffs Have Expanded; The Strike Zone Might Have, Too.

Written by: Justin Choi (@justinochoi)

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Is the playoff strike zone a bit bigger? In general, yes – it’s been confirmed by different analyses over the years, including this one by Jeff Sullivan written in 2017. But in 2018 and 2019, playoff strike zones became tighter relative to their regular season counterparts, reversing an existing trend. 

This year, however, the strike zone might have expanded once again. 

If you’ve been following the endless slate of 3-game wild card series, that may not come as a surprise. There have been numerous games in which an umpire’s discretion became a source of controversy. In Game 2 of the Dodgers-Brewers series, Brandon Woodruff was ejected after disagreeing with an outside pitch to Austin Barnes that was not called a strike. Zach Davies and Austin Nola of the Padres put up a masterclass in umpire deception. And the White Sox dugout chirped throughout A’s pitcher Chris Bassitt’s start, which included indefensible calls such as this: 

But during the postseason, when the stakes are higher and so are tensions, it’s easier to remember the egregious calls than it is to appreciate the fair ones. Emotions could be clouding our perception of umpire performance this season. 

Can we quantity, for the sake of objectivity, the nature of a strike zone? On Baseball Savant, the zone is divided into four quadrants: the Heart, Shadow, Chase, and Waste. The Heart is the very center of the zone, whereas the Shadow represents its edges. A generous zone, therefore, would consist of called strikes in the Shadow in addition to the Heart. 

We can calculate the rate of called strikes in the Shadow, with taken pitches as the denominator. By comparing this to the league-wide, regular season rates, we can get a rough estimate of how stingy or liberal a postseason strike zone is. Going back ten years, here’s how those rates have fluctuated:

Over ten years, the rates are more or less similar, yet there are noticeable patterns. The regular season called strike rate has steadily increased. There’s no concrete explanation as to why, but I suspect it’s mainly due to an emphasis on pitch framing, a skill that until recently had not received a sabermetric quantification. Or maybe pitchers are better than ever, thus more adept at exploiting the edges of the strike zone. But that’s for a later article. 

In contrast, though the playoff called strike rate has fluctuated year-by-year, it always stayed above the regular season rate – that is, until the previous two years. It’s unclear why the trend has reversed. If anything, you would think better framing would induce more called strikes. 

Finally, let’s examine 2020. For the first time since 2016, the league-wide called strike rate has decreased, yet the playoff called strike rate is up – quite dramatically too. It’s the biggest jump since 2014, when the rate inexplicably shot up above 49%. The gap right now between the regular season and the playoffs is 1.7 percentage points. That may not seem like much, but that’s at least tens of pitches, some of them crucial to the outcome of a given game. Brushing this change off as variance, I think, would be wrong. 

Here’s another aspect to consider. It’s been argued that the reason for an uptick postseason called strikes is the improved crop of pitchers. Better pitchers receive the benefit of the doubt. But according to this logic, shouldn’t the expanded postseason, which includes teams with mediocre pitching, have lowered the rate of called strikes? 

We also can’t point fingers at a few notorious individuals – that risks including confounding variables, and besides, Ángel Hernández didn’t umpire a wild card series game. 

Perhaps it’s a bit too early to draw any conclusions. We still have the Division Series, Championship Series, and ultimately the World Series, during which a correction can occur. But still, that there are this many extra called strikes, this early into the postseason, is worth our attention. If the current rate stands, it’ll be the first postseason since pitch tracking began in 2008 to have a borderline called strike rate above 50%. 

This made me wonder – does the postseason called strike rate depend on the scale and importance of a game? Maybe umpires become more conservative during the World Series, when a wrong call can make or break an entire season. 

To answer this question, I divided each postseason since 2011 into two groups: one includes only Wild Card and Division Series games; the other contains Championship and World Series games. If my hypothesis is true, we would see a higher called strike rate in the latter group: 

That is the case between 2012 and 2014, but all other years showed a greater concentration of borderline strikes in Wild Card and Division Series games. Of course, this doesn’t imply that the 2020 postseason will follow any sort of existing trend – the called strike rate for the remaining games can be, realistically, anywhere between 44 and 52 percent. 

I also considered whether pitchers were simply throwing more pitches around the edges. But over our 10-year sample, the percentage of those pitches hovered around 42 to 44 percent, a minuscule range that fails to explain neither the increase in called strikes nor illustrate an overall trend. 

What we do know is that we are in the midst of the first ever postseason, at least since 2011, in which pitches on the edges of the zone are called a strike over half the time. There are conflicting factors here. Better framing and better pitchers suggest that this change is explainable. But the expanded playoffs and a sudden jump from two stagnant years, 2018 and 2019, add an element of mystery. 

Ultimately, I do think it boils down to pitchers, with the help of their battery-mates, creating a better zone for themselves. There are probably smaller factors I’ve failed to consider. But in the grand scheme of pitch calling, their significance is questionable. 

Follow P365 MLB and KBO Analyst Justin Choi on Twitter! @justinochoi

Follow us on Twitter! @Prospects365

All statistics from Baseball Savant

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