Where Did the Homers Go?

On Monday, I examined the new baseball’s impact on April home run totals. In sum, home runs were down in April 2021 compared to April 2019, with the home run per batted ball rate dropping by roughly 0.45 percentage points, a figure that would result in about an 8% decrease in home runs from ’19 to ’21, under the assumption that hitters receive roughly equal plate appearances in each season. (Due to seven-inning doubleheaders and the new extra inning rules, though, that won’t happen, but it’s still good to compare apples-to-apples to estimate the impact.)

After sharing the article on Twitter, I received an interesting question that I felt merited further discussion: How many of those now-non-homers turn into hits versus outs? That is a fascinating question because it potentially gets to the heart of why MLB dejuiced the baseballs in the first place. Baseball didn’t want to eliminate offense, per se; they just wanted to alter how it is generated, with more balls put into play rather than what they perceived as a recent over-reliance on the long ball. In short, if all of those newly-created non-homers are now other types of hits, then dejuicing the baseball might’ve actually had the impact MLB wanted. If they are now outs, then it’s just going to make life that much harder for batters.

Given the majors’ historically-low batting average this season — once again, I’ll point you to Brendan Gawlowski’s excellent piece on the matter — you can likely guess what happened: Outs are up.

Just to make the data familiar again, here’s the heatmap that compares the probability of hitting a home run based on launch angle and exit velocity bins that I created. This shows, for example, that when hitters hit fly balls with a 100-104 mph exit velocity and at a 20-24 degree launch angle, they were rewarded with a home run at a rate that was 34 points higher in 2019 than ’21:

This group — the 100-104 mph EV, 20-24 degree LA — is the area where I want to first draw your attention. Within this subset of the data, I evaluated the distribution of outcomes for hitters in both 2019 and ’21. While these distributions are wholly dependent on where I set the bounds of the bins — meaning that, if you set your bins differently, the distributions would look different as well — a comparison remains useful. Since we’re maintaining consistency across the two different seasons, we can underscore the importance of the changes. So while an individual season’s distribution is quite dependent on the bins, the comparison is less so.

With that out of the way, here’s the distribution of outcomes for these types of batted balls in 2021:

And now here’s the distribution of outcomes in 2019:

That is a rather stark change. While a home run was the most common event for these types of batted balls in 2019 by far, it’s the third-most common this season. It’s good that we’re still seeing a base hit — doubles — leading the way here, but the real story is the “field out” group. In 2019, fly balls hit between 100-104 mph and at a 20-24 degree launch angle went for outs (including sac flies) just 18% of the time; using the inverse, hitters would reach base 82% of the time when they’d connect. In 2021, however, hitters are reaching base just 65% of the time. That’s still a solid figure, but it provides further evidence that, rather than convert home runs into other types of base hits, MLB has only reduced offense overall. That’s not a shocking conclusion, but at least it is consistent.

I looked at the three other groups with at least a 15-point decrease in home run probability, and the outcomes were practically identical. In every case, the new ball is not creating more hits. Here is what those reach base probabilities look like:

Unsurprisingly, in all of the bins most affected by the new baseball, we’re witnessing an associated decline in the overall probability the batter will reach base. We know how good defensives have become; if more balls are staying in the yard, it was always extraordinarily unlikely that they’ll be going for hits at the same rates. But to see a 32-point decline, as in the example of the 95-99 mph exit velocity, 20-24 degree launch angle bin, is striking. Batters were more often than not reaching base on those types of batted balls in April 2019. In April 2021, they only reached base one in five times.

More generally, you’ll notice once again that most of the affected batted balls are those below 30 degrees in launch angle. This makes sense, considering this type of contact — lower-hit fly balls — would be most impacted by an increase in drag when hitting a home run is a binary, “Did it go over the wall?” question. (Meaning that, even if higher-hit baseballs aren’t going as far, they’re just not going as many rows back into the seats.) To get a larger sample for our distributions, we can compare all fly balls below 30 degrees, irrespective of exit velocity, and have more than 1,000 batted balls to analyze.

Here’s 2021:

And now 2019:

The effect is the same. Home runs are down, outs are up. Batters reached base on 54% of fly balls hit at a launch angle below 30 degrees in April 2021, down 11 points compared to April 2019, when they reached base 65% of the time.

Ultimately, the proof is right here: de-juicing the baseball, even if it was slight, likely did not have the impact that MLB was expecting. If baseball’s higher-ups are interested in more singles, doubles and triples, changing the baseball (at least so far) has not proved helpful in that regard. All we’ve seen is an overall decrease in offense; when strikeouts are increasing at the rate that they are, and defense is as good as it is, limiting hitters’ main tool to counteract excellent pitching probably only will serve to backfire overall. While balls are still flying over the fence quite frequently, the decrease in offense is likely here to stay under these new conditions.