The Effect of Additional Called Strikes with the Expanding Strike Zone

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Mike Napoli and John Farrell have stated that the strike zone has continued to grow in 2015. Ian York previously looked at this and determined that Mike Napoli has been subjected to additional strike calls in the early part of 2015. In this article, he looks at other players around Major League Baseball to see if additional called strikes with the expanding strike zone has impacted certain players more than others.

Since 2010, the strike zone has been getting bigger. It had large increases in size from 2010 to 2011, and from 2013 to 2014; in both those years, the zone expanded at the bottom, while the sides, if anything, became slightly narrower. Right-handed batters took the brunt of this expansion, with their strike zone becoming significantly larger than that of left-handed batters. The decline in baseball offense over the same period is at least partly related to the larger strike zone.

It’s too early to be very confident in changes from 2014 to 2015, but the early results show that the zone is still expanding. It appears the outer edge of the strike zone may be getting wider, especially to right-handed batters.

That means that each year since 2010, batters have had to learn the strike zone anew at the beginning of each season. Pitches that in 2013 would be called balls, are called strikes in 2014. The difference is not great – a matter of an inch or two each year – but baseball is a game of inches. For many batters, the change in strike zone boundaries is not a major distraction. Either they learn the new zone quickly, or their playing style is less affected by small changes in zone boundaries.

Nevertheless, this effect is real. Mike Napoli, who has complained about having wide strikes called on him, is correct; he has had strikes called on him this year that are outside the strike zone as it was called in 2014, and he has had more of these than the average player. On the other hand, the actual number of these calls has been fairly small – only about 10 pitches this year fall into that category, meaning that nearly 95% of the called strikes on him would also have been called strikes last year (or, in some cases, would have also been simply bad calls, well outside the strike zone; frustrating, but not an effect of the changing strike zone). While it’s undoubtedly true that each of these “out-of-zone” called strikes must have add-on effects by making Napoli doubt each subsequent swing decision, his overall performance this year can’t be put entirely on the changing strike zone. (Nor has he tried to blame the changing zone, simply pointing to it as one source of frustration.)

We can look across Major League Baseball at other hitters to see who is more and less affected by the changes in strike zones over the years, and to see how others have adjusted to the changes. To do this, I focused on 2014, because we know the final strike zone shape and size for both 2013 and 2014. We do not have enough data to confidently describe the 2015 zone at this time. I used PITCHf/x data for all these calculations, and it is important to keep in mind that PITCHf/x is not 100% reliable. The rare errors in PITCHf/x usually tend to even out, but we are looking at rare events to start with, so a single mistake could lead to an incorrect number.

I used qualified batters (over 502 plate appearances in 2014). (Mike Napoli did not have enough plate appearances in 2014 to qualify, so he is not in the following numbers. If we were to use a cutoff of 200 PA, allowing Napoli to qualify, he would be in about the top 20% of batters – severely affected, but far from the worst.) I limited the data to called strikes only, and asked which called strikes in 2014 both fell within the strike zone for 2014, and fell outside the zone as it was called in 2013 (for brevity, I will call these “out of zone strikes”, “OOZ”, even though they are actually inside the 2014 zone). The average for all these 146 batters was 2.5%. Here are the top and bottom five batters (the full list is here):

Stands Called strikes OOZ OOZ Percent
Top 5 Yunel Escobar R 304 22 7.2
Ian Kinsler R 484 27 5.6
Jose Altuve R 370 19 5.1
Andrew McCutchen R 394 19 4.8
Trevor Plouffe R 426 20 4.7
Bottom 5 Luis Valbuena L 376 3 0.8
Denard Span L 516 4 0.8
Evan Longoria R 426 3 0.7
Adrian Gonzalez L 319 2 0.6
Brian McCann L 392 2 0.5

One obvious point jumps out from this table. The top five are all righties; four of the bottom five are lefties. In fact, RHB are far more affected than LHB in general. The average OOZ percent for RHB was 3.1%; for LHB, 1.7%. Nineteen of the twenty most affected batters are RHB; eighteen of the twenty least affected are LHB. Here is the distribution of OOZ calls:

The strike zone for right-handed batters has increased disproportionately compared to left-handed batters, and so there is more area in which a strike can be called.

Even within the right-handed batters, Yunel Escobar is an outlier. His OOZ percent of 7.2% is nearly 30% higher than the second-highest batter. Here are those pitches that fell into the “OOZ” category in 2014; the 2013 strike zone is outlined in grey, the 2014 zone in red. The green contour map shows where all the pitches he saw in 2014 ended up:


From 2013 to 2014, the strike zone expanded downward about an inch and a half. Pitchers threw Escobar many pitches in that 1.5 inches, and he didn’t swing at 22 of them that were called strikes.

That sounds bad, and it probably is. An extra 22 called strikes is not inconsequential, especially since every unexpected strike call throws doubt into the batter’s mind. But 22 called strikes over the course of a full season is not actually a very large number. Looking at all the batters, how much impact on offensive production do these OOZ calls have?

Surprisingly little, it turns out. Here is the plot of batters’ out-of-zone percentages compared to their wRC+:

The effect becomes more apparent if we look only at right-handed batters, but it is still quite small:

The overall offensive contribution of a batter may be slightly affected by the proportion of out-of-zone called strikes he sees, but the effect is small. In a perfect world, we could look at individual batters’ wRC+ with a consistent strike zone year to year, and with the changing zone. However, too many other factors affect a batter from one year to the next for this to be helpful in our statistically imperfect universe.

Does that mean Napoli (or other batters) are wrong to complain about the changing zone and its effect on their batting? Not at all; the effect is real and it truly is a handicap to batters, especially right-handed batters. But it would be unreasonable to blame one’s overall contribution to this small effect. Napoli specifically said that the changing zone was a source of frustration, but was not responsible for this year’s struggles, which seems to be as balanced and accurate a statement as he could make.


Follow Ian on Twitter @iayork.

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Ian is an immunologist and virologist who lives in Atlanta with his wife and two sons. Most of his time is spent driving his kids to baseball and soccer games, during which he indoctrinates his children on the glories of Pedro Martinez, the many virtues of the Montreal Expos, and other important information.

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