Spotlight: Ronald Acuña Jr.

Ronald Acuña Jr. vs. the field. It was a legitimate question entering the season, at least per the results of Ron Shandler's Twitter poll last September:



Nearly two months into the season, that coin-flip result would point overwhelmingly towards the field, as Acuña is barely squeaking inside the Top 50. That's almost entirely buoyed by his running game too—Acuña ranks 5th in the majors with 14 SB—as his batting average has dropped nearly 100 points with just 3 HR and 12 RBI (not a typo!) through his first 198 PA. Let's kick off our analysis in traditional Facts/Flukes form:


20241983/ - .253/.23812/7150/23/263311678/838%8%14387%28%


A few things to highlight as a jumping off point for our deeper dive:

  • Acuña has given back all of 2023's massive contact gains (ct%), which in tandem with a sudden loss of hard contact (PX, HctX) has combined to torpedo his xBA. Acuña has fully "deserved" 2024's lower batting average.
  • The power outage is fully deserved as well, as Acuña's underlying xPX is in lockstep with PX, he's hitting fewer fly balls (FB%), and he's posting a single-digit barrel rate for the first time in his career.
  • The "speed never slumps" cliché is holding true here, however. Acuña has a full green light (SBO) when he does get on base, and he's taking full advantage (SB%).


Let the deep dive begin. We'll focus on the drastic changes to Acuña's contact rate and what might be driving the early power outage.

Plate skills

While it's easy to home in on Acuña's 2024 skills, let's take the long view and play a quick (and easy!) game of Can You Spot the Outlier? 

Here are Acuña's contact rates (ct%) by season throughout his career, excluding 2020:



Besides the obvious question of "who captured Acuña and replaced him with Tony Gwynn last year?", let this be a cautionary tale when trusting a single data point over a player's established track record, even if it lasts a full season. Let's look at some plate discipline metrics to see just what's changed over the last few seasons:




  • Acuña's swing decisions remain mostly unchanged. He doesn't chase much outside the zone (O-Swing%; league-average 31%) with just a minor uptick in in-zone swings (Z-Swing%).
  • But he's whiffing a ton. Acuña's contact within the zone (Z-Contact%; league-average 85%) has sunk to new lows—well off the league average of 85%—while his out-of-zone whiffs have gone right back to 2021-22 levels.
  • A career-high swinging-strike rate (SwK%; league-average 11%) sums things up well; this is a different hitter than we saw last year, and fully deserves the contact rate falling back from 2023's peak.


Trouble with the fastball

Acuña is being pitched to differently this season too, which could be driving that uptick in whiffs. Check out the number of fastballs he's seeing in 2024 compared to recent seasons:



And it's not just the number of fastballs, but where they're being thrown as well. Here's a heatmap of fastball location to Acuña from 2023 (left) to 2024 (right). He's seeing a healthier dose of heaters up and in:



Below we see Acuña's performance against those fastballs, which is where we see the real collapse:




  • Acuña hasn't been able to handle this new up/in location—his whiff rate has doubled against fastballs vs. last season, and is well above what we saw in 2022.
  • PutAway%, which is the rate of two-strike pitches that result in a strikeout, shows that pitchers aren't afraid to challenge Acuña with a heater on two strikes. And they're being plenty successful.
  • The power metrics (EV, xSLG) say that even when Acuña does make contact, there's been little oomph compared to previous seasons.


Where'd the power go?

We could throw another chart up here of more detailed Statcast metrics than the xPX and Barrel% noted in our initial skill scan above, but they will all tell the same story: Acuña's simply not hitting the ball hard. But taking the long view, along the lines of our Where's the Outlier? game earlier around his contact rate, let's do a similar exercise for Acuña's barrel rate over the years:



Acuña's track record of excellent power can't be ignored, and if we're going to preach track record over a single data point, there's an obvious case to be made that this early outage is just a slump, and will positively regress back to normal over time. There might be a caveat, though…


… is he hurt?

The one elephant in the room we haven't addressed yet: the possibility of a hidden injury. Acuña struck fear in fantasy managers this offseason with an irritated meniscus—likely an extended side effect from knee surgery in 2021. Our own Matt Cederholm addressed the issue in a March 7 Big Hurt column, giving Acuña a 2 (out of 5) score on our "Worry-O-Meter" scale with the following conclusion:

It’s also likely he has micro tears in the meniscus that are causing the irritation, so there’s increased risk going forward. It’s probably not enough risk to knock him out of the #1 spot, but it’s there.

We do have some reference for how Acuña fared the last time coming off that knee issue—his 2022 campaign that yielded just 15 HR and a .266 BA in 537 PA. The injury oddly didn't affect his running game, which is what we're seeing in 2024 as well, but the similarities in our key power metrics should be noted, as both are well off from Acuña's career average. 




This is pure speculation of course—we likely won't know the extent to which Acuña's knee is bothering him until after the season—but a similar power outage to what we saw in 2022 is certainly within the range of outcomes.



Let's close through the lens of Acuña's rest-of-season projections (as of Thursday, May 23), which properly balance a player's track record/skills entering the season with year-to-date performance. Given what we've uncovered in our deep dive, a quick game of over/under:

  • .279 batting average: This projection is well below our preseason .304 mark given Acuña's early struggles, but we'll still take the under. Last season's enormous ct% spike looks like a clear outlier, the plate discipline metrics show a disturbing amount of whiffs, and pitchers seem to be attacking a soft spot with more fastballs up and in.
  • 19 home runs: Acuña's power skills are down this year, but the track record is there for him to rebound quickly. We'll take the under by a smidge, however, to account for the possibility that his preseason knee issues are a bigger deal than originally thought. There's a chance Acuña's power production falls back to what we saw in 2022 (15 HR in 537 PA), his first season back from ACL surgery.
  • 33 stolen bases: This one seems about right, particularly if we get any type of positive BA/OBP regression. Acuña is running wild through his slump, and with an 87% success rate, there's no reason to think that won't continue.

Things will get better—Acuña is simply too good (and too young) for this to continue—but for as much of a slam dunk as he was with the first overall pick, this has been a massive disappointment. Closing the loop on our “Acuña vs. the field” poll at the top, Albert Pujols is the only player to repeat as the top overall fantasy player in consecutive seasons (2008, 2009) over the last 20+ years. Your feat is safe for another year, Albert.

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