We all know platoon splits exist for not just hitters, but pitchers.
How do they look?
Non-Contact Outcomes
K% & BB%
Minimum 1000 pitches vs. L/R:
- Average K% diff: 3.98%
- Median K% diff: 3.30%
- Average BB% diff: 2.72%
- Median BB% diff: 2.20%
A typical pitcher would have a 3.3 K% / 2.2 BB% split between left/right-handed hitters, which is significant but does not seem extraordinary.
Correlations
![](https://majorseventh.blog/wp-content/uploads/2021/08/2015-21-Pitcher-K-vs.-R_L-min.1000-1.png)
![](https://majorseventh.blog/wp-content/uploads/2021/08/2015-21-Pitcher-BB-vs.-R_L-min.1000.png)
Pitchers’ strikeout ability transferred between sides; there was a significant correlation(r^2 of 0.382), although I personally was expecting a much higher correlation.
The most radical contrast came from Jordan Romano, who had one of the highest K% vs. LHB(42.5% – 5th) while having merely an average K% vs. RHB(24.3%).
Walk rates had a weak correlation. So much so that Zac Reininger had one of the highest BB% vs. RHB(3.8% – 22nd), while one of the highest BB% vs. LHB(15.2% – 35th).
Results
- Average K-BB% diff: 5.47%
- Median K-BB% diff: 4.55%
Using median K-BB% difference, I used the kwERA equation to convert K-BB% into a potential ERA difference:
12 * 4.55% = 0.546
Meaning: a typical pitcher has a 0.55 ERA-worth of a platoon-split in performance by striking out / walking more or less.
Contact Outcomes
EV & LA
Minimum 100 BIP vs. L/R:
- Average EV diff: 1.77 mph
- Median EV diff: 1.40 mph
- Average LA diff: 3.5°
- Median EV diff: 3.0°
A typical pitcher would have a 1.4 mph / 3° split between left/right-handed hitters, which is also significant but does not seem extraordinary.
Correlations
![](https://majorseventh.blog/wp-content/uploads/2021/08/2015-21-Pitcher-K-vs.-R_L-min.1000.png)
![](https://majorseventh.blog/wp-content/uploads/2021/08/2015-21-Pitcher-LA-vs.-R_L-min.100.png)
A pitcher’s EV-against is entirely specific to the batter’s handedness.
The most radical contrast came from Gregory Soto, who had one of the lowest EV vs. LHB(83.4 mph – 19th) while having one of the highest EV vs. RHB(92.5 mph – 3rd). Correspondingly, the xwOBAcon split was 0.140.
On the other hand, there was a significant correlation between LA R/L, which means that groundball/flyball pitchers are likely to be groundball/flyball pitchers against both sides of the plate.
Results
- Average xwOBAcon diff: 0.033
- Median xwOBAcon diff: 0.028
Using median xwOBAcon difference, I used the dERA equation to convert xwOBA into a potential ERA difference:
0.028 * 28.61 = 0.801
Meaning: a typical pitcher has a 0.8 ERA-worth of difference in performance just by the quality of contact allowed. Interestingly, balls in play created a bigger difference than strikeouts/walks.
A certain portion of the difference is likely due to the hitter, not the pitcher.
![](https://majorseventh.blog/wp-content/uploads/2021/08/2015-21-Pitcher-xwOBAcon-vs.-R_L-min.100-each.png)
Surprise, surprise: there was little correlation between a pitcher’s ability to manage contact against LHB vs. RHB. In other words, a pitcher can be amazing at suppressing LHBs, and simultaneously be terrible at suppressing RHBs.
With xwOBAcon split, Nate Jones comes out of the page with a staggering difference of 0.158(0.475 vs. L, 0.317 vs. R).
It is something worth thinking about that the LA correlation didn’t contribute to the outcome(xwOBAcon).
Cause of Splits
![](https://majorseventh.blog/wp-content/uploads/2021/08/EV-Split-vs.-xwOBAcon-Split.png)
![](https://majorseventh.blog/wp-content/uploads/2021/08/LA-Split-vs.-xwOBAcon-Split.png)
Now, close to half of the difference in xwOBAcon can be explained by EV difference; an r^2 of 0.494 is very significant. For every 2 mph, pitchers gained/lost around 0.026 points.
LA showed a much weaker correlation, For every 5°, pitchers gained/lost around 0.017 points.
![](https://majorseventh.blog/wp-content/uploads/2021/08/LA-Split-vs.-EV-Split-1.png)
![](https://majorseventh.blog/wp-content/uploads/2021/08/2020-21-Avg.±1_2-St.Dev_.-EV-by-LA-1.png)
Some of the EV Split is caused by LA Split; for every 10 degrees, the average EV drops by approx. 2 mph.
This matches with considering that the vast majority of pitchers have an average LA between 5-20°; a decrease in LA results in a much more EV decrease than an increase(about 2x).