Aaron Judge, Paul Goldschmidt, and José Abreu aren’t the only recent MVPs off to underwhelming starts in 2024. After putting together a season for the ages last year, Ronald Acuña Jr. has scuffled thus far, both in terms of making contact and hitting for power. His struggles have coincided with those of a couple of the team’s other heavy hitters, with the result that the team recently slipped out of first place in the NL East for the first time in more than a year.

Roughly two years removed from season-ending surgery to repair a torn ACL, Acuña became the first player ever to hit at least 40 homers and steal at least 70 bases in the same season. He clubbed 41 dingers and swiped a major league-leading 73 bags, aided by a couple of rule changes that increased per-game stolen base rates by 41% league-wide. Playing a career-high 159 games, he hit .337/.416/.596 while leading the NL in on-base percentage, steals, wRC+ (170), plate appearances (735), at-bats (643), total bases (383), hits (217), runs (149), and WAR (9.0). Despite a strong challenge from Mookie Betts, he was a unanimous pick for the NL MVP award.

Where has that electrifying slugger gone? With more than a month of play under his belt this season, Acuña has hit just .267/.373/.359 with 14 steals but just two homers. Thanks to his 12.4% walk rate and his high on-base percentage, that slash line is still good for a 116 wRC+, but the 54-point drop in wRC+ is steep, even if it’s “only” the 16th-largest in the majors among players with at least 400 PA last year and 100 this year.

Exactly what’s going on with Acuña is unclear, but it may well be health-related, as he had a scare early in spring training. Following a rundown during a February 29 game against the Twins, he felt soreness in his surgically repaired right knee, which led to an examination by Dr. Neal ElAttrache, the orthopedic surgeon who repaired his torn ACL in 2021. Dr. ElAttrache found only irritation in the meniscus of the knee, but that was still enough to sideline Acuña for two weeks as he rested before resuming his preparation for the season.

We haven’t heard much about the knee since, so setting it aside for the moment and merely focusing on his performance, two things are glaringly apparent. First, he’s swinging and missing much more often than in 2023, and is particularly struggling against four-seam fastballs. And second, he isn’t hitting the ball nearly as hard, or in ways that can do as much damage.

Because Acuña had already come close to a 40-homer, 40-steal season in 2019, finishing with 41 homers and 37 steals, it was easy to focus on his combination of the two counting stats and wonder just how high he could go in the latter category given the larger bases and limitations on pickoff throws introduced in 2023. Less obvious was his dramatic reduction in strikeout rate. He went from striking out 23.6% of the time in 2022 — matching a career low set the year before, down from the 26.4% rate he struck out over his first three seasons — to 11.4%. Per MLB.com’s Mike Petriello, his 12.2-point drop was the second-largest in AL/NL history, behind only the 12.4-point drop of light-hitting Orioles shortstop Mark Belanger, from 21.5% in 1968 to 9.1% in ’69.

Belanger’s improvement was aided by the league-wide redefinition of the strike zone in the wake of the Year of the Pitcher, but Acuña didn’t have that working in his favor. Instead, he just didn’t miss as often, cutting his swinging strike rate from 10.9% to 7.8% and improving his zone contact rate from 83% in 2022 to 87.8% in ’23. So far this year, he’s given all of those gains back and more. He’s making contact on just 78.1% of pitches in the strike zone, his lowest mark since 2020, and his swinging strike rate is a career-high 13.4%. Both his 15.4-point jump in strikeout rate and his 5.9-point jump in swinging strike rate are the majors’ largest, and he’s already got 12 multi-strikeout games, up from 10 for all of last season. All of this has happened despite relatively little change in Acuña’s chase rate; per Sports Info Solutions, he went from 28.5% in 2022 to 26.8% in ’23 and is back up to 28.9% this year.

Here’s a look at Acuña’s whiff rate by Gameday Zone, based on data through May 6. Keep an eye on that upper row:

As you can see from those charts, Acuña was vulnerable to pitches in the upper third of the strike zone and higher; he shored up that weakness in 2023, but has regressed. Here’s a fuller look at his results on pitches in that area, with 2021 data thrown in as well:

Acuña punished those high pitches last year, but he’s getting absolutely dominated by them this year, with his whiff rate nearly doubling and his quality of contact just terrible. Pitchers appear to have caught on, because they’re putting a higher percentage of them in that vicinity. They’re mostly fastballs; last year, 53.6% were four-seamers and another 20% sinkers, while this year, the percentages are up to 66.4% for the four-seamers and 15.1% for the sinkers.

Less dramatically, Acuña has fallen off against pitches on the outer third of the plate and further outside, though the effect is more subtle. Including only the ones that are in the strike zone (Gameday zones 3, 6, and 9 for those of you scoring at home), he’s gone from hitting .318 and slugging .588 in 2023 to hitting .409 and slugging .682 this year, but his whiff rate has climbed from 22.3% to 36.1% on those pitches. If we include the ones that are outside the strike zone (Gameday zones 12 and 14), it’s a different story, in that he’s gone from .292 AVG/.505 SLG with a 29.1% whiff rate to a .220 AVG/.340 SLG with a 43.4% whiff rate. He’s chasing all varieties of pitches outside the zone, and having much less success at bad-ball hitting in general. Including those that are inside the inner third of the zone, he’s slipped from a .252 AVG/.405 SLG (.441 wOBA) with a 31.8% whiff rate to a .111 AVG/.156 SLG (.297 wOBA) with a 45.9% whiff rate. Cripes.

Pitch-wise, as that increasing percentage of high fastballs suggests, Acuña’s fall-off has been particularly acute when it comes to four-seamers, regardless of location:

I don’t know about you, but I had to pick my jaw up off the floor looking at the overall 2023 versus ’24 splits, as well as the location-based ones. Even on four-seamers in the strike zone, Acuña’s whiff rate has more than doubled relative to last season, his wOBA on such pitches has fallen by more than 50 points, and his barrel rate has been more than cut in half. Outside the zone, he hasn’t collected a single hit on a four-seamer this year, after feasting upon them last year.

Which brings us to Acuña’s quality of contact, which has gone from top shelf to merely pretty good:

Last year, Acuña was in the 93rd percentile in barrel rate, the 98th percentile in hard-hit rate, and the 100th percentile in average exit velocity and the expected stats. This year, he’s well above average in most of those categories, but it’s still a very different picture:

Woof. The loss of power is particularly notable, and you can see from the bars further down how badly he fares when it comes to whiffs and strikeouts. The only category where his percentile ranking has improved is in walk rate.

I didn’t show it above, but it’s worth noting that Acuña’s not hitting it in the air as often as last year. His groundball rate has increased from 49.5% (which was a career high) to 51.6%, with his fly ball rate dropping from 30.4% (which was a career low) to 24.2%. His groundball-to-fly ball ratio has increased from 1.63 to 2.14, even while his average launch angle has increased slightly from 7.4 degrees to 8.5. His sweet spot rate — the percentage of batted balls hit with launch angles ranging from eight to 32 degrees — has dropped only slightly, from 33.6% to 31.9%, but it has dropped nonetheless.

If I hadn’t pulled up Acuña’s numbers and charts myself, I’d have a hard time believing that the 2023 and ’24 ones are from the same player. As to the why, I don’t know whether his problems are mechanical, health-related, psychological, or a mix of all three, and as always, I’m reluctant to speculate. Nonetheless, it’s striking the way Acuña’s 2023 numbers resemble his blazing pre-injury half-season in ’21, while his comparatively mediocre ’24 numbers bear closer resemblance to his tentative return in ’22, which puts me in mind of this quote from late in that season:

Ronald Acuña Jr.: “It’s all part of the process & I’m hoping for better days. But I have to say, for example, the knee with my swings, it doesn’t always feel the same. Some days I have confidence in it, some days I don’t feel like I have confidence in it, and it’s not the same.”

— David O’Brien (@DOBrienATL) August 5, 2022

We haven’t heard much about Acuña’s knee since he was sidelined, though O’Brien did note that after he attempted a sliding catch in an April 16 game, he walked gingerly and pointed to his right knee when the team’s trainer attended to him, though he stayed in the game. If the joint is bothering him, that still doesn’t explain why his sprint speed percentile ranking is consistent with last year (67th percentile then, 69th now) or why he’s stealing bases at a similar clip. After being thrown out by the Red Sox’s Reese McGuire on Tuesday, he’s 14-for-16, putting him on pace for 69 steals, with his success rate improving from 84% to 88%.

Last week, Acuña did string together three multi-hit games for the first time all season, going a combined 7-for-14 with a double and a homer in one game against the Mariners and two against the Dodgers. But even if you zoom out to squint at some arbitrary endpoints — he’s hitting .381/.409/.571 through the first week of May! — a five-game sample is hardly large enough to be convincing.

Acuña isn’t the only one of the Braves’ top hitters who has opened the season in a funk. Matt Olson has dropped from 160 to 91 in terms of wRC+, Austin Riley from 127 to 104, and Michael Harris II from 115 to 96. Still, none of those falloffs are as dramatic as Acuña’s, or are happening to a player who’s on the short list of the game’s best. Absent a clear explanation, I’d guess that his right knee is a major factor in what’s going on, but until Acuña offers us more insight, we’ll just have to wonder what’s happened to the 2023 NL MVP.