The importance of swinging strike rate and why I’m buying Dan Straily and Blake Snell

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Kim Klement (USA Today Sports)

On one hand pitching is an extremely complex endeavor, with the prospect of success and failure straddling the finest of lines. The difference between a strike and a ball, or a whiff and a home run, rests on mere inches. Not only that, but if one aspect of the pitcher is amiss, whether it be his arm strength, mental focus or delivery mechanics, the results can be devastating.

But on the other pitching is also very simple. Success as a pitcher really boils down to three things: striking batters out, avoiding walks and keeping the ball on the ground. You can spend days analyzing the minutiae of release points and pitch sequencing, but in the end it’s all for the benefit of getting whiffs, staying in the strike zone and avoiding hard hit fly balls.

Strikeout percentage (strikeouts divided by batters faced) alone explains 50% of starting pitcher ERA (based on a regression analysis run covering starting pitchers from 2015 to 2017). That’s kind of amazing, because strikeout percentage says nothing directly about the quality of contact a pitcher gives up, his ability to pitch through jams and a variety of other more subjective elements of pitcher skill. Yet it still gets us half of the way there in terms of explaining pitcher performance (one thing to note is that strikeout percentage implicitly factors in a pitcher’s efficiency in getting outs, since increasing the denominator, batters faced, would result in a lower percentage).

The diligent fantasy manager will certainly place importance on strikeout percentage when selecting their pitchers. Not only do strikeouts have a tremendous effect on predicting ERA and WHIP, they often have their own statistical category reserved for them in fantasy match-ups. But the trouble with strikeout percentage is twofold: a) it’s probably the first or second stat everyone looks at, so you don’t derive any arbitrage opportunity by evaluating it and b) it’s a stat that can jump around a bit in smaller sample sizes.

For instance, a pitcher might benefit from a string of pitcher-friendly umpires who call a lot of borderline strikes, leading to more strikeouts. Or maybe a pitcher is often paired with a catcher skilled in pitch framing, giving the pitcher a disproportionate share of called strikes and thus strikeouts. In these cases, and as well as out of sheer randomness, looking at strikeout alone can deceive.

That’s where swinging strike rate (SwStr%) comes in. Measured byswstr FanGraphs as swings and misses divided by total pitches, SwStr% is the holy grail of advanced pitching metrics, and a rare case where the stat nerds and the old school baseball geezers see eye to eye on things. Everyone loves the visceral thrill inspired by Corey Kluber inducing a pool noodle hack on his nasty slurveball, right? Well it also turns out that Kluber’s ability to do that is precisely what makes him so good. Kluber led the MLB in SwStrk% last season at 15.6%, and the rest of the top 10 is dotted with names like Max Scherzer, Chris Sale and Clayton Kershaw. Needless to say, SwStrk% matters, and it matters a lot.

In fact, by itself, SwStrk% explains 37% of of a pitcher’s ERA. It does this while having little to no relationship with the other primary drivers of ERA, including walk rate, home run rate and batting average on plays in play (BABIP), making it a truly independent and predictive statistic. And because the sample of swinging strikes in a given game is much higher than the sample of strikeouts, it’s a statistic that stabilizes quicker, making it very useful for unearthing pitching talent prior to when the full-scale breakout in strikeouts and ERA occurs.

Now with all that exposition out of the way, let’s take a look at two pitchers who were SwStr% surgers in the second half of 2017 and thus should be on your fantasy radar heading into the 2018 season.

Dan Straily (MIA)

Straily has kicked around for the last two years as a good but not great fantasy option who likely oscillated between last pitcher on the roster and streaming candidate for most managers. Straily was a former top prospect with the Oakland Athletics, where he made his full-time MLB debut with 152 innings in and 3.96 ERA 2013. He battled ineffectiveness the following two seasons and bounced around from the Astros to the Padres to the Reds, where he finally settled down and turned in a decent 2016 season.

Just when Straily was getting used to Cincinnati, he was dealt to the Marlins in January 2017 for Luis Castillo (man, I like Straily, but looks like the Marlins were in the business of making bad trades before Jeter came along…). Going from the band boxy Great American Ballpark to Marlins Park is a great move for a hurler, but Straily’s results were mixed. His ERA / FIP / xFIP slash was a mediocre 4.26 / 4.58 / 4.70, although he did see improvement in his strikeout and walk rates compared to the previous year. Straily also demonstrated an improvement in his SwStr%, which increased from a roughly average 10.2% in 2016 to a top 15 mark of 12.1% last year. Straily’s ability to induce whiffs also got stronger as the reason wore along, with an 11.7% rate in the first half compared to 12.8% in the second half.


Straily’s 2017 pitch mix, with corresponding whiff rates. (Source: Brooks Baseball)

Straily plies his craft with a four pitch mix that includes a fourseam fastball, slider, change and the occasional curveball. The slider is a definite plus pitch, generating whiffs over 18% of the time it’s thrown and holding hitters to a 389 slugging percentage against. He throws the slider close to 30% of the time but could probably stand to use it more given just how effective it is. Straily’s changeup is also a plus offering, with a SwStr% in the 17-18% range. The fastball is Straily’s weak spot, generating a 500+ SLGA and 250+ isolated slugging against the last two seasons.

Straily, despite his flaws (poor fastball, too many home runs), is a pitcher that could be on the cusp of figuring things out. He has two plus offerings in his slider and changeup and could stand to use them more, creating potential strikeout upside. His home ballpark is also one of the most pitcher friendly in baseball. If things shake right for Straily, I can envision a 3.75 ERA with a 9.0 K/9, which would make him a bargain at his laughably low ADP of 425.

Blake Snell (TBR)

Snell was drafted in 2011 by Tampa and took a methodical path through their minor league system, spending multiple years in rookie ball, A ball and high-A before graduating to the upper minors. Snell really made a name for himself in 2015 when he, across A+, AA and AAA, posted respective ERAs of 0.00, 1.57 and 1.83. That performance earned him the #12 mark on Baseball America’s top prospect list heading into the 2016 season.

Snell followed that up with a terrific 2016, splitting time between AAA Durham and and Tampa. Snell pitched 89 major league innings that year with a 3.54 ERA and K/9 nearing 10.0, tantalizing Rays fans and fantasy owners alike. Despite Snell’s penchant for walking a few too many batters (10% rates across most of his minor league stops as well as his MLB call-up), the raw stuff and strikeout ability seemed to win out…

Until the beginning of last year. Snell’s first half was abysmal, with a 4.85 ERA plus FIP and xFIP estimators above 5.00. His strikeout rate sank below 20% and his walk rate hovered in the mid-teens. Not surprisingly, Snell also wasn’t displaying the ability to induce whiffs with the same frequency, as his SwStr% sank to 8.8% in the first half.


The owner a traditional four-pitch mix that includes a fourseam fastball, slider, curveball and changeup, all with use percentages in the double digits, Snell made an adjustment in the second half to rely less on his fourseamer, which he was throwing above 60% of the time to start the year, and more on his breaking pitches, particularly his changeup and curveball.

The results were stark. Snell’s numbers improved across the board, with a 3.49 second-half ERA and markedly improved strikeout and walk rates. His SwStr% increased from 8.8% in the first half to 12.4% in the second, which put him just outside the top 10 among MLB starters. The shift makes sense, as Snell generates well above average swings and misses on all his offspeed offerings, particularly his slider and curveball. Meanwhile, his fastball generated a paltry 5.5% SwStr% last season and gave up a slugging rate above 500.

If there was any doubt Snell had locked down a rotation spot with his fantastic end to 2017, the departure of Jake Odorizzi to the Twins all but ensured it. Snell, now 25 and coming off over 170 innings pitched last season, is also likely free of any innings or pitch limits. The walks might present an issue at times, but Snell is well within reach  of a 3.65 ERA and a K/9 above 9.50. ESPN has him ranked as the 247th player on the draft board, only 12 spots above Tyler Chatwood. That’s crazy. Take Snell in the 20th round of your draft and be ready to profit once the season kicks in.


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