Which one of these is not like the other?
It’s a list of the current Reds bullpen pitchers sorted by the statistic of strikeout percentage minus walk percentage (K%-BB%) for the 2018 season. I included the major league average for relief pitchers to provide context.
Why focus on strikeouts and walks? Here’s a succinct explanation offered at FanGraphs:
We care about strikeout and walk rates for two primary reasons. First, pitchers have a lot of control over their strikeout and walk rates which means that they are a decent measure of pitcher performance and skills. Strikeouts and walks aren’t the only aspects of pitching, but they are two aspects of pitching which are mostly attributable to the pitcher rather than the pitcher and their team combined.
Second, strikeouts and walks are important because they are stable predictors of success. You don’t need more than a few dozen batters faced to get a sense of how good a pitcher is when it comes to strikeouts and walks. Obviously talent changes and opponents matters, but pitchers who collect strikeouts routinely prevent runs and pitchers who allow walks typically allow more runs and you can get a sense of where a pitcher stands pretty quickly when using K% and BB%.
Overall, the numbers show the Reds bullpen has been pretty, pretty good.
Sure, there has been culling. (You might want to hide the bottom row of the next chart from the kids.)
Otherwise, Tanner Rainey and Zack Weiss were pressed into temporary duty and didn’t do well in limited opportunity. Kevin Shackelford made four decent appearances (18.5%-7.4% = 11.1%). Cody Reed got into three games as a reliever, with three strikeouts and no walks. And that’s been it for Reds bullpen, well, plus Cliff Pennington’s one inning.
But let’s get back to Wandy Peralta. Peralta’s performance stands out among otherwise excellent numbers for the bullpen, and not in a good way. That’s not just a this-year thing, either. Over his past 33 appearances, dating to August 26, 2017, his walk rate has equalled his strikeout rate. Both are 18.2%. Peralta has nearly double the walks and a third fewer strikeouts as the average major league reliever.
Wandy Peralta had a spectacular month of April 2017. Over 12 appearances and 11.2 innings, he struck out 17 batters and walked just two. That’s a Chapman-like rate of 41.5% for strikeouts. But the other five months of 2017 Peralta’s numbers were below average: 18.0 K% and 9.9 BB%.
In certain quarters, the narrative never caught up with reality. Peralta didn’t have a breakthrough season in 2017. He didn’t establish himself as an above-average reliever, worthy of assignment to high leverage innings. The chance that his scintillating first month in 2017 was a fluke is something that should have been given serious consideration by the middle of last year. It should have been the conventional wisdom about Peralta by the offseason.
Almost every reliever is fraught with significant variability. Peralta’s last year or so is an extreme case. As Reds fans, we have to hope he’ll be able to replicate April 2017 again.
But the clear-eyed bottom line is that other than one month in the past two seasons, Wandy Peralta has been mediocre-to-awful.
Should he be kept around to fill the role of a situational left-handed pitcher? The problem is, Peralta doesn’t really do that. His performance splits are small: wOBA of .293 vs. LH batters and .311 vs. RH batters in 2018. He had an even smaller handedness split gap in 2017.
When Michael Lorenzen makes his welcome return in the next week or so, Wandy Peralta is clearly the pitcher who should be demoted.