How would a proposed MLB change to the lower part of the strike zone affect the Pittsburgh Pirates?
It’s been well documented that the lower part of the strike zone has gradually expanded in the last seven years. With more changes being heavily considered, how will the Pittsburgh Pirates hitters and pitchers be affected by a potential shift?
Jon Roegele of The Hardball Times published an excellent analysis of this phenomena near the end of last season. His methodology was to find the point where 50 percent of taken pitches were called strikes and 50 percent were called balls and labelled that the edge of the strike zone. This approach shows that the bottom part of the strike zone has expanded by 45 square inches since the 2009 season. And, not surprisingly, the strikeout rate has grown and the walk rate has dropped throughout this time frame. Major League Baseball has taken notice and has proposed strike zone changes that will bring the bottom of the zone from “the hollow beneath the kneecap” to “the top of the hitter’s knees”, effectively raising the zone by an estimated two vertical inches.
What effect would this change have on the Pittsburgh Pirates? Would it be positive or negative? We will take a look at overall team offense followed by some detail about each starting pitcher.
First, we need to take a look at the Pittsburgh Pirates team strikeout and walk rates during this period of low strike expansion. The table below shows data compiled by The Hardball Times overlaid with Pirates non-pitcher hitting statistics from the same period.
|Year||Strike Zone Size (sq. in)||Strike Zone Size Below 21” (sq. in)||MLB K%||Pirates K%||MLB BB%||Pirates BB%|
Sources: The Hardball Times, Baseball Reference. Pirates data is for non-pitchers only
Since this table compares all of MLB to only the non-pitchers of the Pirates, we can’t say that the Pirates strikeout more or less than MLB overall. However, we can look at the trends over time and draw some conclusions. We see that the Pirates K percent correlates well with the strike zone expansion and the overall MLB K%. However, when we look at the BB%, we see that the Pirates non-pitchers were walking at a rate less than the MLB average in 2009 and 2010, but starting in 2011 (the Clint Hurdle era), the walk rate has gone up while the rest of MLB walk rates have dropped, presumably due to the expanded strike zone.
Even though the differences are small, over 5000+ plate appearances, the effects of a half a percent of BB percent will be big. From this data we can conclude that, as a team, even though the Pirates are piling up Ks with the rest of MLB, they have continued to get more than their fair share of walks even though the strike zone has grown considerably. With a proven ability to get in base via a walk, it would be reasonable to expect the Pirates’ walk rate to increase much more than the league average with a relaxed strike zone.
It goes without saying that shrinking the strike zone will adversely affect pitchers. To understand the severity of the change on the Pirates pitching staff, we first look at the top four known starters. These pitchers will, hopefully, pitch the most innings for the club and be the most affected by the new strike zone.
If we split the strike zone horizontally into thirds, we can parse the pitch data and see how often each pitcher throws in the bottom third of the zone. According to Baseball Analysts, the average percentage of pitches thrown in the lower third of the strike zone is 15 percent and doesn’t change much for a LHP or RHP. Note that this does not include all low pitches – many are in the dirt, inside or outside. We are not trying to judge the ability of a pitcher to throw an inside pitch, only trying to see how often they throw a strike in that lower third of the zone.
Then we can analyze the rate at which those pitches are taken (not swung at). It’s hard to measure for all pitchers combined, but the average across MLB is approximately 35 percent. So if we have a pitcher who throws more often than average in the lower third of the strike zone and those pitches are taken at a higher rate than average, then you can infer that pitcher’s walk percentage will go up more than the league average under the new strike zone rules. You can also reasonably assume that some of those walks would have been backwards K strikeouts under the “old” strike zone rules.
Let’s look at Pittsburgh Pirates “ace” Gerrit Cole. Over the last three seasons, Cole threw 1166 pitches in the lower third of the strike zone. This equates to 15.9% of all pitches that he threw, so he is slightly above average in throwing low. The opposing batters “took” these pitches 40% of the time, which is well above the average of 35%. Unless Cole makes an adjustment, his walk rates will increase more than the average pitcher in 2017 with a proportionately lower decrease in called strikeouts. Cole has walked only 6.2% of the batters he has faced during his career and, based on this math, we could very well see a number north of 8% in 2017 if the new strike zone takes effect.
This same analysis can be repeated for the other known Pirates starters and is shown in the table below.
|% of pitches thrown in lower third of strike zone||
% of pitches in the lower third of the strike zone taken by the hitter
Jameson Taillon is set up to be the least impacted by the reduced strike zone. He throws low in the zone less than average and is about average when it comes to hitters passing on those pitches. Nova throws low more often than average but this will be somewhat mitigated because hitters swing at more of his low strike offerings. Kuhl has too small of a sample size to draw any meaningful conclusions, but if his early numbers are an indication of 2017, he could be in the same boat as Cole.
Overall Neutral Effect
You may have noticed that we have only carved out the lower third of the strike zone, which is larger than the two vertical inches MLB is talking about taking away from the pitchers. However, the analysis remains entirely valid for two reasons. First, pitch location tends to be concentrated towards the outer rim of the strike zone because pitchers are trying to throw there and most of them are good at their jobs. Second, take rates on pitch offerings on very low strikes are likely to be higher than take rates on the total offerings in the whole lower third of the strike zone. So, the overall effect is likely to be even more pronounced that our analysis shows.
Based on this data, Cole will suffer the most from a revised strike zone with less area available for low strikes. Cole is likely to see his walk rate increase at a higher rate than the league average. Taillon will benefit, relatively, from the change. Sure he will issue more walks overall due to the tightened strike zone, but the percent increase will be less than league average. Nova will probably come in around league average and Kuhl is really anybody’s guess. All four pitchers, barring injury, will start an equal number of games, so the overall effect on the Pirates is likely to be slightly negative.
Compare this to Jake Arrieta, who threw low strikes exactly 15% of the time over the last three seasons, yet saw a high 42% take rate on those pitches. Without making adjustments, he is likely to increase his walk rate even more than Cole. Of course, good pitchers make adjustments all the time as they are getting to know a particular umpire’s strike zone. Cole, Arrieta and the rest of the MLB will undoubtedly make adjustments as well.
Image Credit – Daniel Decker Photography