The place Have All of the Residence Runs Gone? It’s Too Early to Inform

One of many quite a few the reason why Mike Trout’s newest harm — a torn meniscus in his left knee, requiring surgical procedure that may sideline him for at the very least 4 weeks and maybe longer — is such a bummer is that the three-time MVP and future Corridor of Famer was off to a fairly robust begin. Whereas his .220/.325/.541 slash line is nothing to write down residence about inside the context of his profession — certainly, his 141 wRC+ could be his second-lowest mark, after final yr — he had hit 10 homers earlier than the tip of April for simply the second time (2018 was the opposite). That whole was sufficient to share the key league lead with Gunnar Henderson, and it put him on tempo to problem his profession excessive of 45 homers, set in 2019. Even inside an offensive profile that’s present process some evolution as he ages, that’s spectacular.

That goes doubly on condition that by means of the tip of April, league-wide residence run charges had been down greater than 15% relative to final season. The place in 2023 groups averaged 1.21 residence runs per sport, by means of the tip of April that they had averaged simply 1.02 homers per sport. Observe that we’re nonetheless early sufficient within the season {that a} single day’s slate of video games can bump that final decimal in a single path or one other; with 20 homers in 30 team-games on Could 1, the season-to-date common fell from 1.018 homers per sport to 1.007. All of which is to say that whereas the scenario deserves a better look — notably with league-wide scoring having decreased from final yr — this needs to be thought-about a preliminary investigation.

If the house run charge from this March and April holds up — and hereafter, I’m going to lump all video games earlier than Could 1 into what we think about April, simply as we do in our splits — it might signify the most important year-to-year drop since 1987–88, when the per-game charge fell from 1.06 homers per sport to 0.76. If you happen to’ve been following together with residence run historical past, that the 1987 season was an outlier that marked the primary time residence run charges rose above 1.0 per sport. Whereas charges instantly fell again beneath that threshold and remained there by means of the subsequent half-decade, that season served as a preview of what was to come back from 1994–2009, when residence run charges had been above that threshold yearly, seemingly attributable to a confluence of things that ranged from growth and newer ballparks to the widespread use of performance-enhancing medicine and adjustments to the baseball itself.

Final yr’s per-game residence run charge was the fifth highest of all time, however behind 4 different latest seasons:

Based mostly upon the information by means of April 30, this yr’s charge can hardly be thought-about an historic low, but when it held, it might rank as one of many 10 lowest of the Wild Card period:

It isn’t simply residence runs which might be down, both. By the tip of April, scoring was down a bit over 5% relative to final season as groups fell from plating 4.62 runs per sport to 4.38. Batting averages had dropped eight factors (from .248 to .240) and on-base percentages six factors (from .320 to .314). Slugging share plummeted 29 factors (from .414 to .385) — we haven’t seen the league-wide slugging share this low since 1992 — and with one other day of information, it fell to .383. Perhaps commissioner Rob Manfred and his pals can provide you with some guidelines that may assist stimulate offense. Wait, they did that already? What the hell?

Earlier than we get too far into the weeds, it’s value remembering that April (and the tip of March) options the good temperatures of the baseball season, when the ball doesn’t carry as far. Through Baseball Reference’s Stathead, final yr there have been 146 video games that started with temperatures of fifty levels Fahrenheit or decrease, and 133 of these occurred inside a crew’s first 30 video games of the season, which started on March 30. Thus it’s extra useful to match apples to apples, and Aprils to Aprils, and as soon as we do, we see that these residence run charges persistently lag behind the full-season ones:

To protect the graph’s continuity, I included the “full” 2020 knowledge for the 60-game season, however when you ignore that time, you possibly can see that the latest April residence run charges are slightly predictive of full-season charges:

Relative to final April, residence run charges fell 9.8%, a large drop however not the 15.6% slip we get by evaluating the primary month to the earlier full season, with its extra homer-conducive warm-weather months. Given the typical hole between the April and full season charges over this era (0.097 homers per crew per sport) and the usual deviation (0.033 homers per sport), we should always count on this yr’s full charge to land within the 1.083–1.148 vary. At 1.116 homers per sport, the middle of that vary would signify a 7.6% fall-off from final yr, with the extremes at 4.9% and 10.3%.

Something in that vary would signify smaller year-to-year adjustments than we’ve seen within the post-pandemic interval, but it surely’s nonetheless sufficient to advantage a better look. So what’s occurring? Variations in offensive ranges and strikeout charges can cut back the variety of batted balls and subsequently residence runs, however even with what we noticed in April (decrease scoring but in addition a barely decrease strikeout charge), there have been truly extra fly balls per sport this April than final (6.65 vs. 6.57) — it’s simply that these fly balls haven’t traveled as far or achieved as a lot harm. Right here’s the comparability of this season to latest full-season numbers:

Balls are being hit nearly as exhausting as final yr, however they’re not going for singles, extra-base hits, or homers as usually. In actual fact, in the event that they held up for the remainder of the season, the batting common and slugging share on fly balls by means of April could be the bottom since 2016 (.224 AVG, .709 SLG). Once more, it makes extra sense to match solely the April segments:

With that comparability, we see that even on the similar common exit velocity, the typical fly ball carried about two ft lower than the comparable time final yr, however one foot greater than in 2022, with the related charge stats — each precise and anticipated — nearer to the sooner season, which is to say that these fly balls had been much less productive.

This raises the query of whether or not the ball itself has modified, one thing we all know has occurred a number of instances in latest seasons. Modifications involving the yarn, capsule, leather-based, and drying course of — which may change the seam peak, leather-based smoothness, and bounciness of the ball — have been properly documented through the years regardless of Main League Baseball’s lack of transparency. The league’s buy of about 25% of Rawlings, the ball’s producer, appears to have accelerated the tempo of change. Generally, a number of makes of the ball have been used throughout the identical season, and fairly presumably in the identical sport, given the anecdotes of pitchers reporting ball-to-ball variability. As documented by Insider’s Bradford William Davis, with analysis by Dr. Meredith Wills, apparently three totally different variations of the ball had been utilized in 2022.

Early final yr, when residence run charges had been on the rise relative to 2022 — when Aaron Decide nonetheless broke the long-standing American League residence run report with 62 — Rob Arthur reported that the balls’ drag coefficient — as estimated from Statcast pitch monitoring knowledge primarily based on a technique developed by Alan Nathan and David Kagan — had decreased from 2022, portending a rise in residence run charges. Per knowledge now printed at Baseball Savant’s Drag Dashboard, we are able to see that the drag coefficient did enhance considerably because the season went on:

The ultimate estimated imply drag coefficient (.3417) nonetheless wound up decrease than in 2022 (.3469); the .0052 lower was fairly shut in magnitude to the rise from ’21 to ’22 (.0058), however the change went within the different path. The rise up to now this season relative to 2023 is far smaller:

In response to that Savant dashboard, “As a common rule of thumb, a lower within the drag coefficient of 0.01 will enhance the gap of a batted ball with an exit velocity of 100 mph by roughly 5 ft (and a rise of 0.01 will lower batted ball distance by 5 ft).” Apart from the change from 2019 to the shortened ’20 season, not one of the annual adjustments rise to that threshold, and the present one is a full order of magnitude smaller. Based mostly on the reported knowledge, the change in drag isn’t sufficient to account for what we’re seeing, notably given MLB’s notoriously free tolerances in its ball specs. Because the web page notes, “[W]hile drag fluctuates from yr to yr, these adjustments are small relative to the ball-to-ball variation noticed inside a person season… Relative to this small distinction, the usual deviations of the drag coefficients are massive.”

Past drag, adjustments within the ball’s coefficient of restitution and weight, as affected by the humidity stage, also can have an effect on the habits of the ball. In 2022, the usage of humidors turned necessary for all 30 groups, the place solely 10 used them the yr earlier than; these in any respect places moreover Coors Area are set to 70 levels and 57% relative humidity (it’s 62% at Coors). However as a result of humidity ranges range all through the season, even with such controls, the COR will range as properly.

Dr. Wills has begun gathering 2024 baseballs to dissect, however for the second we don’t have sufficient proof to recommend that the ball has modified, and even when it had, that’s to not say such change is intentional. For as essential as Dr. Wills has been of MLB’s lack of transparency in recent times, she acknowledged to FanGraphs, “These form of systematic variations appear to occur once they transfer from one manufacturing cycle to the subsequent. It’s the type of factor you may count on with provide turnover and equipment refurbishment.” Past that, variations in temperature, humidity, wind, and different environmental components could possibly be contributing to what nonetheless counts as a relatively small change in common fly ball distance, and likewise variable efficiency components akin to launch and spray angles.

All of that is one more reminder that we’re nonetheless early within the season. Current historical past tells us that we now have sufficient knowledge to know that we’ll wind up with a decrease league-wide residence run charge this yr than final, albeit to not the intense we’ve seen up to now. And whereas our appreciation of the league’s residence run charge could also be subjective (not everybody desires extra homers), it’s cheap to hope that Trout will return quickly sufficient to do his small half — and likewise, thumpers akin to Decide and Matt Olson, who’re off to gradual begins — in ensuring that it doesn’t drop any additional.