May 2021 Starting Pitcher Skills Surgers

We know that pitchers’ skill levels could change quickly, so it’s important to pay attention. A pitcher could suddenly gain/lose velocity, alter his pitch mix, adjust his mechanics, etc, and suddenly become a new version of himself. So let’s dive into the starting pitchers who improved their SIERA marks most from April to May, driven by a significant improvement in skill metrics.

Way atop the SIERA improvers is Tarik Skubal, who I discussed more in-depth yesterday. As a former top prospect with insane minor league strikeout rates, I take this May breakout seriously.

Wowzers, check out that walk rate improvement by Austin Gomber! From a crazy 18.4% mark in April all the way down to a 2.9% in May. His strikeout rate improved in May too, but the drop in SIERA was primarily due to that walk rate. The April mark was inflated by two four-walk games, plus a disastrous seven-walk effort in his first start of the season. Amazingly in May, he hasn’t walked more than one batter in a game and has mixed in two zero walk games. As is often the case, his true skill level from a walk rate perspective is probably somewhere in the middle. Control tends to come and go and his season walk rate of 9.5% looks right in line with expectations. Because he calls Coors Field home, he’s likely to end the season with an ERA higher than his SIERA, so I’d say he’s right about where he should be from a results perspective.

Corey Kluber had dramatically rebounded in May, reminding us of the elite pitcher he once was. Too bad he’s on the IL now with a shoulder injury.

A 3.3% walk rate for Robbie Ray?! Say it isn’t so! We could usually at least count on strikeouts for Ray, but he didn’t even do that in April. Everything turned around in May though as the strikeouts returned, but they also came along with some unexpected sterling control. With double digit walk rates in four straight seasons and a career mark in double digits, it’s hard to buy into this sudden massive control improvement. Obviously if he could continue, he’ll return to being a strong fantasy asset. But it’s going to be impossible to predict whether this level of control is actually sustainable all season long.

Nick Pivetta is another who saw a massive improvement in walk rate from April to May. Even with that improvement, his walk rate still remains in double digits and well above his career average. A fortunate 6.8% HR/FB rate, which is less than half his career mark, explains how he has outperformed his SIERA for the season, but perhaps an improved walk rate could stave off any ERA increase when the homers increase.

Zack Wheeler was already pretty good in April, but he has taken his skills to an entirely new level in May. Aside from the tiny 3% walk rate, he’s pushed his strikeout rate well over 30%. He hasn’t gained velocity and the only pitch mix change he’s made is switch out some changeup usage for his sinker, which wouldn’t typically result in more strikeouts. So there doesn’t seem to be any obvious reason for the results improvement, which might make it less sustainable.

Patrick Corbin’s strikeout rate barely improved in May after being well down in April, but it was his walk rate improvement that primarily drove that decline in SIERA. There was little reason to expect him to maintain a double digit mark if he was healthy and sure enough, it quickly regressed in May. I don’t think there was really any change here, but rather just a bad spell with his control that got corrected. Bottom line here is that without the strikeouts from his 2018 and 2019 peak, he’s no more than a dice roll with your fingers crossed in AL-Only leagues.