May 2021 Starting Pitcher Velocity Gainers

Pitchers change their underlying talent/skill levels much more frequently and quickly than hitters do. That’s because it could be as simple as gaining/losing velocity or altering their pitch mix. One way to get ahead of the crowd in identifying changing talent levels is by comparing in-season fastball velocity. So let’s find out which starting pitchers have gained the most fastball velocity in May versus April. I included their respective strikeout rates and SwStk% marks so we could see if the added velocity has already resulted in more punchouts.

Zach Plesac stands tied atop the velocity gainers board and his May velocity is now back to where it stood during his 2019 debut. Unfortunately, his strikeout rate, which tumbled in April, has barely moved up in May, even with the nice velocity bump. It’s also pretty surprising to see healthy SwStk% marks with strikeout rates below 20%. Obviously, with a 3.56 ERA, there’s no buying before improvement potential here. Instead, Plesac will have to either improve that strikeout rate to move more in line with his SwStk%, or his ERA is going to jump, as it’s hard to imagine he maintains a .221 BABIP all season, even though he came close during last year’s short season.

Jack Flaherty’s velocity was down in April, but he’s come all the way back, and now his May velocity actually sits higher than any of his previous full seasons. It’s boosted both his SwStk% and strikeout rates. So far over his career, he’s a perfect example of how important it is to monitor the luck metrics. Even though his SIERA has remained pretty stable, finishing between 3.57 and 3.89 since 2018, his ERA since 2018 has gone 3.34, 2.75, 4.91, and 2.47. He was an obvious buy after last year’s unlucky performance, but how the fortune has turned in the opposite direction. However, it’s interesting to note that his career BABIP stands at an impressive .255, so perhaps he does own some suppression skills. That would be pretty surprising though considering a career LD% of 23.1%, which is above the league average. A career 454.4 innings isn’t quite enough to declare those skills are real though, so I’d still bet that BABIP rises and his ERA jumps over 3.00 soon enough.

Did you wonder whether Yusei Kikuchi would carry over his velocity spike from last year? Not only did his April prove it was no fluke, but he’s been even higher in May. And check out that strikeout rate surge and SwStk% spike this month! Last year, he allowed a slightly higher than league average BABIP, but mostly struggled with runners on base, as evidenced by his sub-60% LOB%. This year, both those metrics are fine, but now he has struggled with the home run. If everything comes together, that ERA should finally drop below 4.00 to match his vastly improved skills. He’s the first true buy on this list.

At age 36, Max Scherzer wants you to know that he’s not suffering from age-related decline. His velocity was down in April, but the May spike matches where he has sat the last couple of years. Usually, pitchers his age see annual declines in velocity, but not Scherzer. His skills remain as elite as always, so it’s just a matter of health cooperating.

A decline in velocity last year led to a collapse in strikeout rate and a disappointing season for Patrick Corbin. This season, his velocity has already partially rebounded in April, but took another step up so far this month. In fact, his May velocity has been higher than he finished with since 2017. It hasn’t done a whole lot for his strikeout rate though, but it’s still a good sign and suggests his owners should probably stick with him and hope for the best.

No one really had a clue what we would get out of Corey Kluber this year as he had pitched just 36.2 innings since 2018. His control has been uncharacteristically an issue, but the strikeouts have been back in May. He barely throws his fastball, so the velocity change doesn’t mean as much as other pitchers, but it remains down compared to prior years. With a SIERA nearly a full run higher than his actual ERA, I wouldn’t bet on this success continuing, but he looks like a better bet than the pessimistic view.

Spencer Turnbull has done the unthinkable — increase his velocity, while simultaneously losing his ability to induce whiffs and strike batters out! That May velocity is higher than any of his previous seasons, so I would have to think the strikeouts will return. Also, that strikeout rate is being pulled down by the just one he generated over 25 batters during his first start in May. He makes for an intriguing name to watch.

What the heck is up with Luis Castillo?! With his velocity bouncing back above 97 MPH, there’s no excuse for the lack of whiffs and strikeouts. All of his pitches have generated lesser SwStk% marks, so it’s not like we could point to just one pitch as the culprit. Obviously, he’s been unlucky with a .380 BABIP, which has pushed down his LOB% to just 51.2%. But we obviously expected better than a 4.46 SIERA and far more strikeouts. He looks like a great target for a bottom dwelling team that needs to take a risk with massive upside to move into the money.