Balls are Flying Out of the Yard Again, For Judge, Alonso, and Everybody Else

Aaron Judge is at it again. On Tuesday night in Seattle, the reigning AL MVP and home run king clubbed a towering solo shot off Darren McCaughan to aid the Yankees’ 10–2 win over the Mariners and to continue his latest rampage. It was his fourth homer in three days, his 12th in his past 16 games, and his AL-leading 18th overall. With that, he’s matched his total through the end of May last year, doing so in 46 games, one fewer than in 2022, though the Yankees have played 57 games, leaving him still behind the full-season pace he set en route to an AL-record 62 homers.

Even with this binge, Judge doesn’t lead the majors in homers. Hell, he doesn’t even lead New York City in homers. That honor belongs to Pete Alonso, who’s hit 20. Though he hasn’t homered since Saturday against the Rockies, the Mets first baseman has hit 14 since May 9, the day Judge came off the injured list after missing 10 games due to a minor hip problem. Here’s Saturday’s homer, which came at the expense of Chase Anderson:

Now that we’ve enjoyed some dingers, it’s only fair to mention that this article isn’t really about either of the Empire State’s sluggers so much as it is the conditions under which they’re positioning themselves for runs at 50-homer seasons — again. Recall that Judge set a rookie record with 52 in 2017, only to be topped by Alonso with 53 two years later. Balls aren’t flying out of the yard at the pace they did in either of those seasons, which happen to be the two highest full seasons on record; in 2017, teams bashed 1.26 homers per game, and in 2019, they upped that rate to a stratospheric 1.39 per game. This year, teams are averaging 1.15 homers per game, the seventh-highest rate on record (or sixth-highest, if you exclude the pandemic-shortened 2020 season). You have to carry the calculations out to a third decimal to place it properly:

Here’s the reminder that seven of the past eight seasons occupy seven of the top eight spots above. That situation, and the annual fluctuations in home run rates, owes a whole lot to changes in the composition and manufacturing of the ball itself, altering its aerodynamic properties. Those changes — involving the yarn, pill, leather, and drying process — have been well documented over the years despite Major League Baseball’s lack of transparency. The league’s purchase of about 25% of Rawlings, the ball’s manufacturer, seems to have accelerated the pace of change. Sometimes, multiple makes of the ball have been used during the same season, and quite possibly in the same game, given the anecdotes of pitchers reporting ball-to-ball variability. While the varying makes all fall within the rulebook’s official specifications, it’s worth keeping in mind what Dr. Alan Nathan told this reporter for Baseball Prospectus’ Extra Innings book in 2011: “The specs on major league baseballs, they almost don’t deserve to be called specs, they’re so loose that the range of performance from the top end to the bottom end is so different.”

Indeed, despite commissioner Rob Manfred claiming during last year’s All-Star Game festivities that the 2022 season would feature only balls produced under Rawlings’ latest process, reporting by Insider’s Bradford William Davis, aided by research by Dr. Meredith Wills, showed that three different versions of the ball were apparently used. Some lively balls constructed in 2021 were used in ’22, some more deadened balls built for ’22 were used as well, and a “Goldilocks” ball, whose weight and aerodynamic properties fell between those of the other two, turned up, too. As the Insider report noted, a disproportionate number of the baseballs that Wills procured for the purposes of disassembly, measurement, and production code-breaking came from Yankees games, on the road as well as at home. One can speculate that those aided Judge’s chase of Roger Maris’ long-standing single-season AL mark of 61 homers, but the data is hardly complete.

Anyway, as to the 2023 ball. In mid-April, Rob Arthur checked in at Baseball Prospectus with a report that, based on spring training and early regular-season data, the estimated drag coefficient on the balls has decreased from last year, portending an increase in home run rates that falls within the range of recent years:

This year, we’re on track for a baseball that’s roughly as aerodynamic as it was in 2020 and 2021, leading to high but not stratospheric home run numbers.

…Averaging spring and the first week-plus of the regular season, we arrive at a drag coefficient of right around 0.342. This level of drag puts the league almost exactly at parity with the numbers in 2021 and the abbreviated 2020 season. It’s also within spitting distance, albeit so far a little bit higher, than 2018’s drag level—2018 was a brief reprieve from record-setting, sandwiched between the two highest homer seasons of all time, 2017 and 2019. We are still far from those lofty heights, both in terms of drag and the home run rate. The latter won’t become settled until after the warm summer peaks, but at the moment we are on track for something like a 1.2 HR/game average.

Before returning to Arthur’s estimate, it’s worth a Statcast check-in on fly balls:

As noted at the bottom of the table, Statcast and our data provider Sports Info Solutions address pop ups differently, with the former counting them separately from fly balls and the latter including them (and expressing infield fly ball rates as a percentage of fly balls instead of all batted balls). I find this particularly helpful for this context, since we’re interested in how the ball is carrying when it’s hit in the air to the outfield. By Statcast’s estimates, these balls are being hit slightly harder than last year (I’m using the full-season rate here) and traveling a foot further, with a higher percentage leaving the yard. That said, they’re falling three feet shorter than in 2021 even with the same average exit velo. Since this data doesn’t include the warm-weather months, its worth getting back to the early-season comparisons:

This year’s fly balls are carrying an average of two feet further than in the early season last year. The result is a rate of home runs per fly ball that’s 9.5% higher (1.3 percentage points higher) than in 2022. By comparison, this year’s per-game rate is up 7.4% over last year’s full-season rate of 1.07 homers per game and up 14.9% from last year’s early-season rate (1.0 per game).

This year, teams hit 1.13 homers per game in March and April, then 1.18 per game in May to get to that 1.15 per game overall rate, which checks in as the lowest early-season rate — games in April and May, plus the early trickles from March — since 2018. Note that for these comparisons, I’m using May 31 as the cutoff when possible, though for this year, the data cuts off at May 30, which isn’t such a big deal given that the season started on March 30; this year’s sample of 1,652 team-games is the fourth-highest in my 2014–23 set, with last year’s 1,473 the lowest thanks to the lockout-delayed start.

Since the 2020 season didn’t begin until late July, we don’t have data for April/May, so I used the “full” season data — 1,796 games, about three days’ worth of data more than the largest batch in my 2014–23 set — to keep the graph from breaking. As you can see, the early-season rates consistently lag behind the full-season ones, mainly because a higher percentage of games are played in cooler weather, when the ball doesn’t carry as far. Leaving 2020 aside, not since ’14 has the early-season home run rate been higher than the full-season rate — and that was in the lowest season with the lowest home run rate since 1992.

If we’re trying to anticipate where this year’s rate is going to end up, it turns out that the early-season rate plus the average gain from early season to full season aligns with Arthur’s estimate:

Bullseye! Referring back to the first table, this year’s rate of 1.20 homers per team game would mark 2023 as the fifth-highest of all time (fourth-highest if we exclude 2020), surpassing 2000 and 2016 in the rankings.

There are other ways to gauge the fluctuations in home run rate; they don’t move the needle by much more than a decimal point, but they do account for other concurrent changes. For one, since the major league-wide on-base percentage is up eight points from last year, from .312 to .320 (possibly owing to the new rules prohibiting infield shifts, and perhaps the introduction of the pitch clock), teams are taking slightly more plate appearances per game (from 37.46 to 37.83), and so the rate of home runs per plate appearance has risen comparatively less. Where last year batters homered in 2.86% of all plate appearances, they’re doing so in 3.05% this year, an increase of 6.4%. If we’re comparing early-season rates, the rise is from 2.76%, an increase of 13.5%. The graph is basically the same shape as the one above, and likewise when it comes to home runs per batted ball, which is useful when strikeout rates fluctuate. They haven’t done so much this year (22.7%, up from last year’s 22.4%), and so the 7.7% year-over-year rise (from 4.21% to 4.54%) and 14.7% early-season rise (from 3.95%) are both in line with the aforementioned per-game increases. If we’re comparing 2023 to ’14, when the strikeout rate was just 20.4%, it might be of greater use to know that while the per-game home run rate has risen 33.8% in that span, the per batted ball rate has shot up 40.3%.

As for what this means for the five boroughs’ two top sluggers, the data suggests that if similar conditions prevail — similar to what we’ve seen this year, that is, while accounting for warmer weather, and without MLB and Rawlings pulling another midseason switcheroo, a possibility that can’t be discounted — both will have an easier time in chasing 50-plus homers so long as they continue to swing the bat with similar proficiency. Regression always lurks around the corner, and injuries and slumps could slow down their pace, but both hitters have shown they can reach these heights before. Judge’s .691 slugging percentage is five points higher than last year, and his isolated power 13 points higher, and while Alonso’s .558 slugging percentage is 25 points lower than in 2019, his .320 ISO is just three points shy of his rookie season. Still, if we do wind up with The Great New York Home Run Chase of 2023, that fun will owe something to the more favorable conditions under which those hulking sluggers are obliterating baseballs.