May 2021 Starting Pitcher Skills Decliners

Yesterday, I discussed seven starting pitchers whose SIERA marks improved the most in May versus April. Those improvements were driven by underlying skills surges — some sort of combination of a higher strikeout rate, lower walk rate, and/or more optimal batted ball distribution. Let’s now flip to the pitchers whose skills declined the most, leading to the largest increases in SIERA from April to May.

Lance Lynn has made it a habit of outperforming his SIERA, posting an ERA below that mark in five of six seasons since 2014. Most of that is due to an ability to keep his fly balls from flying out of the park, as he has posted single digit HR/FB rates in half of those seasons. This year, he started off April in elite fashion, so his skills for once actually matched with his performance. Unfortunately, it didn’t last, as his May skills deteriorated. Of course, now his season skills are right in line with where they have been the previous two seasons. Aside from the concern stemming from worse pitching in May, his season SIERA sits a whopping 2.35 runs above his ERA! He’s posted massively suppressed BABIP and HR/FB marks and an inflated LOB%, so the good times are coming from every direction. He’s a prime sell candidate in my mind, as he should bring back a really nice hitter.

I enjoyed Anthony DeSclafani’s April, but his May skills took a serious dive. His fastball velocity dipped about half a mile per hour and he didn’t generate as high a SwStk%. Compounding the problem was a spike in walk rate. The good news is that he’s now startable after last year’s 33.2 inning disaster, but I’d feel most comfortable only starting him at home at this point, even though oddly enough, his ERA is significantly higher there at the moment. However, his xFIP is much better at home, but massive differences in BABIP and LOB% are causing the discrepancy and those are likely to correct.

LOL at Gerrit Cole, who amazingly appears third on this list solely because his April was so otherworldly. He went from possibly the best starting pitcher in history with that 1.55 SIERA to just merely one of the best pitchers in baseball.

In April, at age 39, Adam Wainwright was looking like the best he’s ever been. It didn’t last. His season skills are now right back in line with expectations. He lost a bit of velocity in May, which is something that needs to be monitored given his advanced age. I wouldn’t feel very comfortable starting him in even a deep league.

After a strong April, Cristian Javier’s skills declined in May, mostly driven by a sudden lack of control. It’s still surprising that he was moved to the bullpen, as the inflated walk rate was mostly driven by six walks in his final start. Perhaps it was a move to slow down his innings count. Anyway, I’m still confused about how he strikes out so many hitters without an elite SwStk%. Even his CStr% is nothing special. So my skepticism over his strikeout rate, combined with his extreme fly ball rate, makes me cautious on his near-term future.

It looked like Mike Foltynewicz was back as at least a streaming option and certainly an AL-Only asset in April after his velocity collapsed last year, but then he turned into a pumpkin in May as his strikeout rate disappeared. His velocity hasn’t changed much in May, and neither has his pitch mix. Instead, he just generated a ridiculously low 6.6% SwStk% in May, though April’s wasn’t much better at 8.4%. I couldn’t bring myself to start him in any leagues and even if he was a free agent in a deep league, I would prefer a middle reliever to protect my ratios.

After a strong spring training that earned him a rotation spot, Cole Irvin was pretty solid in April. However, his strikeout rate plunged in May and he has become unuseable. His fastball/sinker velocity is down just a tick in May, but he has thrown his changeup far more at the expense of his slider, and switched up some of his sinker for his four-seamer. His changeup has been his best swing and miss pitch, so this would seem to be a good change for his strikeout rate. In fact, his SwStk% was actually up very slightly in May, so it’s bizarre to see such a decline in strikeout rate. The strikeouts should probably rebound most of the way, and with still sterling control, he should get back to earning a bit of AL-Only value.

Given his history, there was no reason to believe that Eduardo Rodriguez would maintain a 2.2% walk rate or anything close to it, and his May walk rate jumped back to where he’s always been in the past. His strikeout rate did decline in May, but his velocity was actually up slightly, and his season mark is now back in line with his history. I don’t think there are any issues here and he in fact makes for a prime target given that his SIERA sits more than two full runs below his ERA, thanks to an insane .374 BABIP, which has helped bring down his LOB% below 70%.