Dane Dunning’s troubles with LH batters

In perusing write-ups on the Texas Rangers’ new starting pitcher, Dane Dunning, and reading evaluations of their trading Lance Lynn to the Chicago White Sox to get Dunning (and minor league lefthander Avery Weems), one thing that I noted in Keith Law’s write-up was a reference to Dunning, a righthanded pitcher, needing to improve against lefthanded batters.

Curious, I went and looked at Dunning’s splits, beginning with his two full seasons in the minors, in 2017 (when he was in A ball, mostly high-A) and 2018 (mostly AA). Here’s his platoon splits for those years:

2017 v. LHB: .243/.306/.422, 28.6% K rate

2017 v. RHB: .224/.289/.300, 27.1% K rate

2018 v. LHB: .256/.338/.349, 24.8% K rate

2018 v. RHB: .221/.276/.271, 29.8% K rate

We see lefties have a little better average against Dunning in those two minor league seasons, but hit for a lot more power — a 199 and 93 ISO for lefties in 2017 and 2018, versus a 65 and 55 ISO for righthanded hitters in those years.

Just as a benchmark, here were the platoon splits for all major leaguers facing righthanded pitchers in 2019:

2019 v. LHB: .254/.331/.444

2019 v. RHB: .247/.312/.423

Lefties had more success than righties against major league righthanders, but the platoon split was not nearly as severe as what we see from Dunning in the minor leagues.

Flash forward to 2020, when Dunning pitched 34 innings, facing a total of 142 batters — 71 lefties and 71 righties, interestingly enough. Here’s his splits in the majors last year:

2020 v. LHB: .246/.352/.393, 22.5% K rate

2020 v. RHB: .152/.211/.242, 26.8% K rate

That is...dramatic. Its a small sample size, but Dunning’s splits, which were large in the minors, got even bigger when he got to the big leagues.

If we look at the Statcast data we see that these dramatic platoon splits are also present in the expected data. Here’s Dunning’s 2020 xwOBA and wOBA against lefties and righties:

Overall wOBA: .264

Overall xwOBA: .287

RHB wOBA: .201

RHB xwOBA: .243

LHB wOBA: .327

LHB xwOBA: .332

In look at these numbers, we see that Dunning outperformed his xwOBA, though his xwOBA of .287 is still better than average (MLB average in 2020 was .315 wOBA and .312 xwOBA). That outperformance was due to his performance against righthanded batters, as his expected and actual performance was basically the same against lefties. And his xwOBA against lefthanders was much, much worse than it was against righthanded batters.

So, yes, Keith’s comments about Dunning needing to improve against lefthanded batters is borne out in the data, both in the minors and in the majors. But how?

Changeups are generally more effective against opposite-handed hitters than breaking balls — breaking balls break away from a same-sided hitter and in to an opposite-handed hitter, while changeups do the reverse. The consensus from reading the prospect writeups on him the past couple of years indicate that Dunning’s changeup trails his breaking ball, and the changeup being a lesser offering makes the splits make some sense.

There’s also the issue of Dunning relying historically more on his two seam fastball than on his four seam fastball. Two seam fastballs (and sinkers) generally are more effective against same-sided hitters and less effective against opposite-handed hitters, due to them having more horizontal break to the glove side, while four seam fastballs have significantly less dramatic splits. Here are the splits against righthanded pitchers for each type in 2019, per Statcast:

4FB v. RHB: .361 xwOBA

4FB v. LHB: .359 xwOBA

2FB v. RHB: .339 xwOBA

2FB v. LHB: .392 xwOBA

SKR v. RHB: .356 xwOBA

SKR v. LHB: .409 xwOBA

Dunning, per the Statcast data, threw 39.4% sinkers* in 2020 and 21.7% sliders — and again, those have been historically identified as his best pitches. He threw 21% four seamers, 11% changeups and 6.8% curves.

* Statcast isn’t bringing any results back when I do leaguewide searches in 2020 for two seam fastballs, so I think the two (which are really pretty similar anyway, and arguably aren’t worth differentiating) may not have been distinguished in 2020 with their data, both pitches being lumped in as “sinkers.”

So, just throw more four seamers and change ups to lefthanded batters and problem solved, right? Perhaps...except that, in looking at the Statcast data, we see that Dunning was already doing that in 2020.

Here’s Dunning’s pitch percentages split out by handedness of the batter:

Dunning was throwing mostly sinkers and sliders to righthanded hitters, with the occasional four seamer mixed in, and mostly ignored his other two pitches. Conversely, he used an almost equal split between sinkers and four seamers against lefties, with the change as his primary offspeed pitch, and the curveball used more often than the slider.

So just throw more four seamers and changeups to lefties and everything will be fine, right? Well, theoretically, yes...however, that assumes a comfort level and ability to command the changeup and four seamer at a level that makes them effective, as well as those pitches being good enough quality pitches to get outs.

Dunning’s slider was his money pitch — he had a 43.5% whiff rate with his slider, and allowed just a .186 xwOBA on it. While Dunning’s changeup was effective — he had a 30.8% whiff rate and a .276 xwOBA with it in 2020 — the results didn’t match his slider results. On the flip side, his four seamer generated many more swings and misses than his sinker — 34.6% of the team batters swung and missed at it, compared to 16.7% for his sinker — and had a comparable xwOBA (.342 for the 4 seamer, .336 for the sinker).

Dunning is not a high spin rate guy, and generally speaking, high spin rate is good for throwing a four seamer, as it results in less drop (and thus a “rising” effect, though the pitch doesn’t actual rise, it just sinks less). That said, I suspect the Rangers’ plan is going to be to have Dunning throw his four seamer more in 2021, particularly against lefthanded pitchers. If Dunning can command his four seamer and changeup, and gets comfortable using them against lefthanded batters, one would expect him to have more success against lefties — something that will be necessary for him to succeed going forward.