In this series, we’re investigating the outcomes when baseball players made what appear to have been New Year’s resolutions to do something differently. But unlike the rest of us, who try to be nicer to our siblings or drink less on weekends, we’re looking here at specific baseball outcomes.

In the first article I considered batters who hit markedly more (or less) to the opposite field in 2016 than in 2015. (Spoiler: It didn’t seem to help much.) In the second one I looked at batters who hit more or fewer balls on the ground. (Second spoiler: While in general batters who hit more in the air and less on the ground improved themselves, the evidence for the players who changed the most—who stuck to their resolutions—shows very limited offensive improvement.)

Next, let’s look at pitchers who allowed more or fewer ground balls.

As I mentioned in my last article, the relationship between ground balls and balls hit in the air is well-established. Ground balls are rarely more than singles at best and get turned into double plays at worst. Fly balls are great if they leave the park, but those that don’t are usually turned into outs. (.074 BABIP. Really.) Line drives are fantastic, but account for only a quarter of balls in play.

Pitchers arguably don’t have as much control over whether their pitches are hit on the ground or in the air, but in reality they have some because the results for pitchers are similar as for hitters. Among the 240 pitchers with 65 or more innings pitched, the top ground-ball machine was Orioles closer Zach Britton, who induced grounders on 80 percent of the batted balls he allowed. Nine other pitchers had a ground-ball rate of 60 percent or higher.

On the other side, Jered Weaver got grounders on only 29.6 percent of batted balls, and seven others were under one-third. Among the 232 batters with 350 or more plate appearances, only four had a ground ball rate over 60 percent but 11 were below 33.3 percent. I could show you histograms and everything, but take my word: Pitchers’ ground-ball rates are pretty much as varied as batters’ are, so they’re worth exploring.

To emphasize, the purpose of this exercise isn’t to determine whether ground-ball pitchers are good or bad. (I litigated that case, from the pitchers’ perspective, in three articles over the summer.) Rather, we’re looking at pitchers who seemingly made New Year’s resolutions to change a year ago, vowing to allow a lot more or a lot fewer grounders in 2016 than in 2015 (and succeeded in doing so). How did it go?

Here are the 10 pitchers with the greatest increase in batted balls hit on the ground. I used a standard of at least 60 innings pitched in both 2015 and 2016. This yielded 175 pitchers, similar to the 185 batters with at least 350 plate appearances in both 2015 and 2016 that I’ve used in the last couple articles. I’ll show their change in ground-ball percentage (ground balls as a percentage of all batted balls) as well as their change in DRA-, which is park- and league-adjusted DRA scaled to 100 (the lower the better):

Well, that went according to plan, didn’t it? The pitchers who got more grounders in 2016 saw their DRA- improve, in several cases dramatically. Only two pitchers got worse in DRA-, and it was negligible for both. PECOTA expected the average DRA for these pitchers to rise by a couple percentage points, so this group clearly did well.

So does that mean that pitchers who greatly decreased their ground-ball percentage saw a decrease in results? Well, yes, it does:

Not that there are any particular superstars on this list, but Hisashi Iwakuma has been an effective starter for Seattle and Ryan Madson had a moment in the sun with the world champion Royals in 2015. Their resolution to allow more batted balls in the air, if they made it, turned out to a bad choice. In fairness, PECOTA pegged every single one of these hurlers for DRA regression in 2016, and given that a couple of them improved their aggregate results were better than expected. But they were still unimpressive.

As I’ve been doing in this series, I’d like to double-check these results, Maybe those top and bottom 10 pitchers are outliers and the overall results are more muted. I checked that by looking at all 175 pitchers who threw at least 60 innings in both years. This list divides them into equally-sized deciles. I calculated the weighted average decrease or increase in ground-ball percentage as well as the weighted average change in DRA-:

I think it’s easier to see what’s going on here with a graph:

This is a stronger relationship than we’ve seen in the past two reports. The red dots run from the upper left to the lower right. The upper left is lower ground-ball percentage, higher DRA-, i.e., worse results for pitchers allowing fewer grounders. The lower right is higher ground-ball percentage, lower DRA-. Those pitchers got more grounders and better results. Case closed?

Well, not exactly. The two dots in the upper left and one in the lower right stand out. They’re saying that pitchers who allowed a lot fewer grounders got a lot worse results, and those that allowed a lot more grounders got a lot better results. Everybody else—seven of the ten deciles—is centered around a change in DRA- of plus or minus five. That’s not much. So I think we can say that allowing a few more grounders or a few more balls in the air doesn’t change things much.

As with New Year’s resolutions, change is hard. If you don’t change, neither will results. But the pitchers who resolve to get a lot more grounders and actually follow through—the pitchers in the first decile—do a lot better. And those that resolve to get a lot fewer grounders, well, they learn a valuable lesson about setting bad goals for themselves. It’s the New Year’s resolution equivalent of resolving to smoke more.

Thank you for reading

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Isn't ground ball rate, or something related to it, a component of DRA? That would explain why there is such a strong relationship.

It actually would be interesting to look at changes in GBR and changes in FIP because FIP explicitly doesn't consider GBR. If there were a relationship, that would imply that we are dealing with correlation and not causation; that an improved GBR is just a reflection of pitching better in general.
Good observation, newsense. Actually, in its first iteration, DRA was mildly biased against groundball pitchers, though that was corrected this year, as Jonathan Judge explained here:

But I like your suggestion and I'm going to look into it. I'll check both ERA and FIP. My prediction: A rising groundball rate will be correlated with an improvement in FIP more than an improvement in ERA, but not for the reason you cited--it's because FIP tends to like groundball pitchers, since they yield fewer home runs. The correlation between FIP-ERA and GBR is -.31, i.e., as GBR increases, FIP decreases relative to ERA.
The major league ERA rose by 0.23 from 2015 to 2016, 3.95 to 4.18. I looked at the top 20 (not just ten) for increased GB%. They averaged, correcting for the overall upward creep in ERA, a 0.28 run decrease in ERA and a 0.36 run decrease in FIP. Pretty good--more grounders, better performance, and as I'd expected, the improvement was more pronounced for FIP, which likes groundball pitchers more than ERA.

On the other side of the spectrum, the 20 pitchers with the largest decrease in GB% averaged a 0.42 run increase in ERA and a 0.17 run increase in FIP. So the increase in ERA was greater. But still, the relationship holds.

I see your correlation/causation point, but I think they're interrelated. Yes, a pitcher doing better in general will have a higher GB% (though there are, of course, counter-examples--Aaron Sanchez was better in 2016 than 2015 with a much lower GB%, while Patrick Corbin went the other way), but by the same token, a pitcher who successfully adds a two-seamer or throws lower in the zone, inducing more grounders, is using ground balls to drive his overall improvement.