Potential Starting Pitcher Strikeout Rate Surgers

A year ago, I developed a regression equation to estimate what a pitcher’s strikeout rate (K%) should be. That formula used a trio of strike type rates found at Baseball Reference, including a pitcher’s looking, swinging and foul strike percentages. While the original formula was a strong estimator, I have since tweaked it slightly.

In addition to the three variables already included, I have added overall strike percentage. This makes sense, as obviously the more strikes a pitcher throws, the higher the probability one of those is the third strike, boosting his strikeout percentage. The new formula is as follows:

xK% = -0.7795 + (Str% * 0.2882) + (L/Str * 1.1695) + (S/Str * 1.4674) + (F/Str * 0.8824)

Adjusted R-Squared: 0.913

The beauty of using this equation is that each metric is on a per-pitch basis. So the denominator grows significantly faster than both plate appearances (the K% denominator) and innings pitched (relating to the K/9 denominator). While we haven’t yet calculated the point at which the metric stabilizes, one would think it does so quicker than the other two strikeout rates, so sample size isn’t as problematic.

Rather than present a straight list of the pitchers whose xK% are most above their actual K%, I have limited it to those with xK% marks of at least 20%. Anything below that just isn’t very exciting to begin with, even if it represents a large jump.

Poor Randall Delgado. He had a prime opportunity to hold down a rotation spot all year in the wake of Patrick Corbin’s elbow injury, and all it took was two poor starts for the Diamondbacks to yank him from the rotation. That’s the type of overreaction a newbie fantasy player makes. His control has been rather terrible, but he has generated a ton of swinging strikes and has induced lots of ground balls. If he ever returns to the rotation, he could earn some NL-Only value.

David Hale started yesterday and his strikeout percentage rose a bit, but it may still remain below his xK%. His control has been suspect as his Str% is low despite a high F-Strike%. He’s struggled with that control at times in the minors, so it’s not guaranteed to be one of his strong points. He should generate lots of grounders once his LD% regresses and be an asset in NL-Only leagues and a streamer option in shallower mixed leagues.

John Danks has flashed career low fastball velocity, though it’s still early, so it could rise near his average last season. His xK% is primarily being driven by a high F/Str percentage, which is the flakiest of the three strike types. He’s posted a career F/Str rate above the league average, but it will likely come down a bit. The good news is that his S/Str rate has rebounded and is sitting at its highest mark since 2009. His respectable Str% also suggests that walk rate is going to come down. I’ll take the under on both of the RoS projections.

Rookie Mariners starter Roenis Elias has generated lots of grounders and his strikeout rate should be respectable. Control has been a problem though, but maybe he could earn a touch of value in AL-Only leagues.

With his outing yesterday, Josh Beckett’s K% should be close to his xK%. Heading into the start, his Str% was down, leading to the high walk rate. But, his velocity has been fine and he has been getting a good rate of swinging strikes. His xK%, though, is being propped up by a ridiculous L/Str rate that has no chance of being sustained.

Rick Porcello has turned foul strikes into swinging strikes, which is an excellent sign moving forward. It has yet to benefit his strikeout rate, but we should see the effects sooner, rather than later.

Jenrry Mejia has gotten a ton of both called and swinging strikes. Yeah, his stuff is good. I still cannot believe that the Mets were seriously pitting him in a battle with Daisuke Matsuzaka for a rotation spot. Don’t worry about the inflated walk rate — his Str% is well above average and suggests that the walk rate is going to decline significantly.

R.A. Dickey’s biggest issue has been a sudden loss of control. His BB% has nearly doubled from last year. The good news is that his strikeout potential remains strong. Given the raised eyebrows I received after I ranked him higher than most expected, I would imagine that he could be acquired rather cheaply if you are the gambling type.