Swinging Against the Tide: Ground-Ball Risers

In the past couple of years, a growing number of MLB hitters have been making some changes. Those changes, to grossly oversimplify, have generally been made in an effort to get the ball in the air more often. Those efforts, epitomized (but again oversimplified) by a term like launch angle, had percolated through baseball for awhile, but have increasingly been galvanized by technologies like Statcast. The rise of Statcast data has more explicitly spurred players to make fruitful adjustments, by way of putting the ball in the air.

Ben Lindbergh and Travis Sawchik, in their book “The MVP Machine”, write about this phenomenon:

“The average launch angle of a batted ball has increased in every year of Statcast: from 10.5 degrees in 2015, to 10.8 in 2016, 11.1 in 2017, and 11.7 in 2018. Over the same span, the rate of balls hit at a 10 degree angle or higher has increased by 3.3 percentage points. According to Baseball Prospectus, the league-wide ground-ball rate in 2018 was the lowest on record, going back to 1950.”

But for every trend, no matter how apparently efficacious, there are those who edge in the opposite direction. Below, those players who have actually, consciously or otherwise, put the ball on the ground more often will be checked in on. 

It should be noted that batted ball percentages require some solid sample sizes to normalize for any given player, sometimes up to or surpassing one hundred plate appearances; the sample of players that follows addresses those concerns by including only players who had qualifying seasons in both 2018 and 2019. That filter, being (to me at least) surprisingly restrictive, leaves us with just 82 players. Also, with that filter comes an obligatory selection issue to highlight: those players who had the chance to reach 500+ PAs in each of the past two years are players who are durable and, more relevantly, proficient enough to warrant that playing time. They were not overly used as parts of platoons, didn’t concede too much playing time to others, and thus are likely part of an “above average” sample of players.

The group described above has been sorted by the year over year change in their ground-ball percentages; this simple strategy is agnostic to line drive rates, the distinction between fly balls and pop ups, etc. Data comes from FanGraphs; if FanGraphs didn’t consider a struck ball explicitly a ground ball, I’ve considered it “in the air”. Before diving into those GB% risers though, featured below is a quick chart on those players who have most dramatically suppressed their ground-ball numbers in the last year. As you’ll see, they’ve done pretty well for themselves.

Well, 2019’s MVPs top the list. Just two players, Rougned Odor and Mike Trout, saw their OPS+ drop despite putting the ball in the air much more in 2019 as compared to 2018. Mike Trout still had a ludicrous season in 2019, and topping a 198 OPS+ in spite of the pressure of statistical regression is a herculean task, even for him. Rougned Odor, meanwhile, batted .205. As a group these players were 41% above average at the plate in 2019. Regardless of their change in GB% though, it’s easy to recognize that this is an exceedingly strong group of players.

As a reader might assume, given the current school of thought related to batted balls, the majority of the 138 examined players experienced a net negative change in ground-ball percentages between 2018 and 2019. To visualize this skewed trend, below is a histogram which buckets those players by their percentage change in GB%.

While not overly lopsided, it does appear fairly clear that ground balls weren’t exactly en vogue in 2019. 50 of 82 players saw a drop in ground-ball percentages from 2018 to 2019. So, those whose ground-ball percentage rose were part of a minority, albeit not such a significant one. 

Below are those qualifying players whose GB% rose at least 5% from season to season, of which there are 19 in total. 

There appears to be a bit of regression to the mean abound, as this group had lower GB%, on (non-weighted, sorry) average, than those fly ball risers. The two groups’ ground-ball percentages, based on their “starting point” in 2018, were perhaps then bound to travel inversely in some cases.

Khris Davis, a paragon of consistency and coming off three straight 40+ home run seasons, saw his ground-ball rate skyrocket while his production fell off sharply. Yoán Moncada, while a big riser in production season to season, was aided along the way by his astronomical BABIP in 2019. Cumulatively, it’s clear that these players didn’t altogether experience a giant leap forward in production from 2018 to 2019.

One interesting note though is the home run totals for this group across seasons: together, this group hit 44 more home runs in 2019 as compared to 2018 despite their heightened ground-ball rates. Kevin Pillar, for instance, exceeded his prior career high while leading the chart above. So did Nick Ahmed. This reality of course makes more sense in the context of the 2019 baseball.

As a final view, below is the top 10 (from the qualifying group of players) ground-ball hitters of 2019, regardless of season-over-season change.

Again, there are big names in this chart, some of which had really strong campaigns in 2019. On the other hand, one has to imagine that the Padres would like to see more loft from Eric Hosmer, on top of the 7% he lopped off his GB% between the past two seasons already. In light of baseball growing understanding of the payoffs from getting the ball in the air, one has to wonder what sort of potential this group might tap into should they make tweaks to their approach.