What Effects Could the Proposed Strike Zone Changes Bring In 2017?

When Bud Selig left the commissioner’s office he left a league in good financial standing, but one that still had some issues. The strike zone and pace of play are two of the on-the-field issues that were discussed recently, and it had some at the SoSH offices asking questionsIan York uses PITCHf/x to answer the question: What effects could the proposed strike zone changes bring in 2017?

Strikeouts in major-league baseball were at their highest level in history in 2015, and are up even more so far in 2016, with 21.1% of plate appearances ending in a strikeout.


In reaction to this, the competition committee at MLB’s owners meetings has apparently proposed a new, smaller strike zone for 2017. The proposed new strike would move the official bottom of the strike zone from the present “hollow beneath the kneecap” to “the top of the hitter’s knees”. A survey of sonsofsamhorn.com writers and editors at sonsofsamhorn.com – all of whom, it goes without saying, are above average in every way – suggests that this would raise the bottom of the strike zone between roughly 3 and 4.5 inches from its present location. For this analysis, let’s assume that the bottom of the zone would be four inches higher.

I used the 2015 PITCHf/x dataset to estimate how this change how this would have affected calls made last season. In these charts (shown from the umpire’s viewpoint) the called strike probability is color-coded, shaded either blue (very low chance of a called strike), green (high probability of a strike), or red (where the probability of a strike being called is close to 50/50). I outlined the de facto strike zone as the grey polygon overlying the red zone, and then added a second outline for the proposed new zone, with its bottom four inches higher.


That’s a fairly substantial difference. If we apply this to pitches thrown in 2016, there would be about a 7% reduction in the number of pitches that fall into the proposed strike zone, compared to the present zone.


Percent of pitches in …
2015 zone Proposed zone
LHB 52.6% 44.9%
RHB 54.8% 47.6%

Of course, that doesn’t mean that the average strike percentage will actually drop 7%, because pitchers will start targeting the new zone, not the old one. And, of course, batters don’t only swing at pitches in the zone.

We can also ask about historical comparisons. PITCHf/x became fully available in 2008, and the strike zone began to expand a couple of years later as shown here, with the bottom making its most dramatic drop between the 2011 and 2012 seasons. A second major drop followed between the 2013 and 2014 seasons, while the size and shape of the strike zone hasn’t changed dramatically between 2014 and 2015. (With the limited data so far available, the zone in 2016 seems to be very similar to that in 2015.) A four-inch boost to the bottom of the strike zone would roll back all these changes, and then some.

Here, I overlay the 2015 strike zone with the 2009 de facto zone (before the bottom dropped out), and the proposed new strike zone:


In 2009, the strikeout rate was 18.0%. The new zone would be a little smaller than in 2009; is it realistic to believe that using that zone would drop the strikeout rate to about 17-18% again?

Probably not. Although the increasing size of the strike zone is undoubtedly one driver of the increased strikeout rate, it isn’t the only one. Strikeouts increased from 2014 to 2015, and again into 2016, even though there was essentially no change in the strike zone during that period. For one thing, pitchers are throwing harder than ever before – the number of pitches per season thrown over 100 mph doubled in that period (553 to 1140).

Still, shrinking the size of the strike zone would almost certainly reduce the number of strikeouts, and a four-inch size change would approximately bring the size of the zone back into the pre-PITCHf/x days, so it could be argued that the change is reasonable. Of course, the problem is adaptation. Batters who have adapted to the gradually changing strike zone would have to adjust back, basically overnight. Skill sets might have to change, and some batters might not be able to make the adjustment. Making the change all at once would be a drastic move, and would undoubtedly have unintended effects beyond the simple increase in offense that the committee is hoping for.

Follow Ian on Twitter @iayork.

All data compiled from PITCHf/x and Baseball-Reference.com.

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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.