Three years ago, I shared with you an updated version of my xK% equation. The formula uses a trio of strike type rates found at Baseball-Reference.com, including a pitcher’s looking, swinging, and foul strike percentages, along with his overall rate of strikes thrown. With an adjusted R-squared of 0.913, it explains a very high percentage of a pitcher’s strikeout rate. Its best use is early in the season when the plate appearance (the K% denominator) sample size is still small, as xK% uses total pitches as the denominator, so we can reach a reasonable sample size to analyze much more quickly.
Below is a cherry picked collection of fantasy relevant starters that posted actual K% marks well below their xK% marks. This would suggest that given a similar set of xK% components in 2017, their actual strikeout rates should rise. And if you ask nicely in the comments, I’ll even go see how my list of 2016 K% upsiders actually ended up doing, and perhaps even post the recap next week!
In the table, I added the league average marks at the bottom, so you have some context. Unfortunately, the league average includes relievers, which definitely boosts S/Str, but I’m not sure how relievers compare to starters in the other two strike type metrics.
No matter how good you think your equation may be, there are always going to be outliers. As a knuckleballer, R.A. Dickey is used to being an outlier and xK% treats him the same way. I have his xK% calculated going back to 2008 (that’s nine seasons!), and every single one of them he has underperformed his xK%. Bizarre. Of course, his appearance atop the list would hardly excite you about his 2017 prospects. Then again, he returns to the National League and a pitcher’s park, sooooo, an interesting deep mixed and NL-Only play?
And we’re two for two folks, as Clay Buchholz has underperformed his xK% in eight of his nine seasons I have on record! Funny enough, he, too, is heading to the National League, though not quite the pitcher friendly venue like Dickey. Buchholz is such a crapshoot, but at least he’s a slightly better crapshoot in the NL. There are worse choices to speculate on during the endgame of your deep mixed or NL-Only league draft/auction.
After enduring his worst performance since his 2009 debut, Jordan Zimmermann must be elated to find himself on a list that offers some glimmer of hope. We could probably blame some of his struggles and disappearing strikeout rate on injury, but not all of it. He needs to get his slider working again and his fastball velocity back to previous levels, but it will be difficult for the 30-year-old to fully rebound, especially in the America League.
Finally we get to the type of name we want to see on these lists…Dylan Bundy. After seemingly being around forever, the one time top prospect finally made it to the Majors for an extended look. He performed admirably and featured a fantastic swing and miss changeup and a fastball that nearly touched 98 mph. His swinging strike rate was well above the league average and he even generated tons of foul strikes, which is the least sustainable strike type. Perhaps this year he’ll turn those foul strikes into more swinging strikes…or, they will result in more balls in play, which would be a negative. He probably can’t be counted on for more than 140-150 innings, but he’s definitely an intriguing breakout candidate.
Bundy started the excitement, and now Mike Foltynewicz continues it. The fireballer is another member of that group of hard throwers who never seem to post strikeout rates commensurate with their velocities. Foltynewicz regularly flirts with the 100 mph plateau, but the pitch’s SwStk% isn’t that much higher than the league average. His favorite secondary pitch is the slider, but it’s just meh, while his curve and changeup have been up and down in generating whiffs. So he’s a real work in progress, but one of those you could imagine the light bulb suddenly turning on for. Given his velocity, you would imagine he has ample upside on the below league average S/Str rate.
Blake Snell is another former top prospect whose 2016 debut looked far better than it truly was. A suppressed HR/FB rate more than offset an inflated BABIP and he ended up posting an ERA about a full run lower than his SIERA. But let’s talk strikeout rate. He had always posted very high marks in the minors, but found the punchout a little more challenging to achieve once he reached the Majors. That said, he actually featured an excellent assortment of pitches. All three of his secondary offerings generated SwStk% marks of at least 13.2%, including an elite slider above 20%. All that resulted in a wonderful S/Str way above the league average. What killed him was simply a lack of strikes. If his pitches are anywhere near as whifftastic this year, then a step forward in control could perhaps push that strikeout rate into the high 20% range. But, that’s a lot to ask from a pitcher with just 89 innings to his name.
Mike Podhorzer is the 2015 Fantasy Sports Writers Association Baseball Writer of the Year. He produces player projections using his own forecasting system and is the author of the eBook Projecting X 2.0: How to Forecast Baseball Player Performance, which teaches you how to project players yourself. His projections helped him win the inaugural 2013 Tout Wars mixed draft league. Follow Mike on Twitter @MikePodhorzer and contact him via email.