Starting Pitcher Strikeout Rate Downside

On Thursday for my American League starting pitching slot, I used my expected strikeout rate metric to determine which starters have the most strikeout rate upside given the components of the equation (strike percentage, along with swinging, looking, and foul strike rates). Today, I’ll look at the starters with strikeout rate downside hinted at by xK%, but expand my group of pitchers to both leagues.

First, a caveat — like any equation, it has trouble at the extremes and typically figures league-leading strikeout rates are going to regress and bottom of the barrel strikeout rates are going to improve. The unweighted average strikeout rate of these top 19 is 24.7%, versus just 18.2% for the 19 most underperforming their xK%.

With that caveat out of the way, it makes it even more shocking and scary to find Ivan Nova atop this list. Not only would one figure a nice strikeout rate spike in his first full season in the National League, but his mark sits at the second lowest of his career, and xK% thinks he’s actually been lucky to achieve even that level! Although he has been throwing strikes, his problem is that a high percentage of those strikes are being put into play. So all of his strike types — swinging, looking, and foul — are below the league average. It all results in a pathetic strikeout rate with some hidden downside if he doesn’t improve upon any of those components. Oh, and with a 4.48 SIERA against a 3.08 ERA, he’s as strong a sell high candidate as any.

This has certainly been a great rebound season for Jeff Samardzija, at least from a skills perspective, but the home run ball hasn’t allowed his ERA to actually prove it. But unfortunately, the career high strikeout rate isn’t exactly real. There’s not much an owner can do about his appearance here, though, as there’s no sell high possibility, unless you’re in a savvy league with owners who rightly focus on SIERA. And even then, your potential trade partner is probably going to demand some discount given the inflated ERA regardless of how much bad luck he knows might be involved.

It’s always amusing to me when players rebound off their worst season to enjoy their best season. That’s exactly what Chris Sale is doing, whose strikeout rate plummeted last year amid a velocity decline. This season, it has surged to a career high, as his velocity has jumped to its second highest mark since he has been a starter. Rather than see his name here and believe him to have been fortunate, think “WOWZERS, even xK% think his strikeout rate should be well over 30%!”.

While it’s never nice to see a pitcher you own in two leagues appear on a negative list, this is another example of spinning Luis Severino’s appearance here positively — that xK% is still five percentage points higher than last year and four over his 2015 debut.

I was down on Carlos Martinez heading into the season, but he has made me look silly. While xK% thinks the strikeout rate surge isn’t completely for real, it still represents quite the surge from previous seasons. Unfortunately, that BABIP isn’t going to remain as low as .260, so the SIERA nearly 0.80 higher is a concern. This is especially true considering that SIERA is built upon a 28%+ strikeout rate, which xK% is leery of him sustaining. I’d sell here, but then again, I was more pessimistic to begin with so I just continue to be wrong!

Ervin Santana’s ERA has finally jumped above 3.00, so the time to sell high has likely already passed. Unfortunately, his ERA is still headed upward, especially if his strikeout rate declines as xK% suggests.

Yeesh, what the heck happened to Matt Cain?! His 4.75 SwStk% is downright hilarious. I think the biggest question is how on Earth has he been allowed to make 16 starts this year and 44 starts since 2015 when his ERA has now sat well over 5.00 every season?

With his strong outing yesterday’s, it’s possible Jake Arrieta’s K%-xK% gap has narrowed. But I did want to bring him up here to note that he’s really been the exact same pitcher he was last year. The only difference has been a bit of gopheritis and a sub-70% LOB% that certainly will rise. He’s obviously also not getting anywhere near the same help from his defense, as his BABIP has skyrocketed from .241 last year to .317 at the moment.