Early Notes on the New Bat Speed Data Release

In the middle of the 2024 season, MLB released bat tracking data for the current year. It was a huge revolution in publicly available data, taking something previously observable but not measurable and turning it into numbers. You can see how hard Giancarlo Stanton swings, but now you can also quantify how different that is from other large hitters. Luis Arraez’s superhuman coordination is obvious from watching him play. But in terms of getting his barrel on the ball, relative to the rest of the league, how superhuman is he? Now we know. I think that public research on this front is likely to deliver more and more insights in the coming years.

Of course, what we all wanted to know about bat speed wasn’t available right away. Namely: How does it change? Was Ronald Acuña Jr.’s disappointing start to the season related to an inability to impact the ball with force? Did Matt Olson’s decline have more to do with bat speed or plate discipline? Also, plenty of non-Braves questions, presumably. In any case, we couldn’t say much about that because all we had were the 2024 numbers.

Guess what: Now we have some 2023 data. MLB and Statcast released 2023 data starting after the All-Star break, the earliest data we’ll ever get because that’s when the bat tracking infrastructure got going. Obviously, we’re also going to get more year-over-year data when the 2025 season starts. But our first crack at multiple seasons of data is still noteworthy, so I set out to look through the numbers and came to a few conclusions. I don’t intend for these to be comprehensive, and I’m sure that a measured and careful approach is going to tease out some new insights that I don’t have. But the data came out yesterday, and here are a few highlights.

Raw Bat Speed Notables

Want a good sign that improving your bat speed isn’t a sure way to improve? The top gainer in bat speed from 2023 to 2024, minimum 100 swings in each year, was Yuli Gurriel. Jordan Walker was sixth on the list. Last season might have been Gurriel’s final one in the majors; Walker went from a 116 wRC+ during his rookie season to a 72 wRC+ last year, and he was a below-average hitter even at Triple-A in 2024. Alex Kirilloff, who just retired at age 27, was in the top 10:

On the other side of the coin, Mark Vientos was one of the biggest decliners in swing speed, but last season he went from Quad-A afterthought to central part of the Mets’ future. Mookie Betts and Bryce Harper had notable swing speed declines and kept on bopping. To be fair, the bottom 10 mostly featured underperformers:

What does this tell us? Clearly, bat speed isn’t constant over time. But also, bat speed isn’t a perfect predictive tool, so it makes sense that a change in bat speed wouldn’t be either. My interpretation is that we’ll need to add some analytical rigor to the pot before getting anything out of this. I think that we’re missing too much of the picture by using only pure swing speed.

Contextual Swings

As MLB data guru Tom Tango pointed out, and as I discussed with my colleague Jordan Rosenblum afterward, we don’t have to restrain ourselves to the aggregate data. Instead of looking at all swings in the aggregate, why not focus on swings where a player made fair contact? The top 10 list doesn’t vary all that much from the one above, but it’s different enough to be interesting:

Likewise, the bottom 10 is similar, but it’s notably missing Betts:

This is arguably a more important skill. It doesn’t matter how hard you hit your foul balls, or how much breeze you produce when you swing and miss. Looking at how this changed from one year to the next is instructive. How instructive? I’m not exactly sure yet. The relationship between change in bat speed on fair contact and change in wRC+ was so weak as to look nonexistent (r-squared of 0.03), but wRC+ data from a half-season is so noisy that I expected that. This is something to keep an eye on as we continue to get new bat speed information.

How should we approach our analysis here as we get more data? I’ll be focusing on how changes in swing speed track changes in production-on-contact metrics. I’m particularly interested in changes in swing speed toward the extremes of the data set. Should we care when sluggers power down more than when average bat speed types do? Does a contact hitter adding swing speed portend an increase in homers? None of that is evident from the 2023 data just yet, but now we can start looking for it.

Injuries

You can see injuries in these data. Betts swung the bat a lot more slowly in 2024, particularly in the second half. Why? He hurt his hand. Fernando Tatis Jr. swung much harder in 2024 than in ’23; guess which year was his first one back
after he missed an entire season with a serious injury. If you’re wondering whether a player is physically compromised, having a past history of how hard he typically swings the bat and a current reading on the same is phenomenally useful. With the benefit of comparing years, we can see that Tatis’s rebound in offensive production coincided with his physical recovery, and that Betts’s sluggish (by his standards) second half included some injury issues. To put a number on it, his average swing speed over the first month after he returned dropped two miles an hour. Hand injuries, ouch!

As we continue to get more data, we can incorporate aging into this assessment. Tango has already done a bit of that here. In that article, he found that swing speed stays roughly consistent through age 31, then begins to decline by between 0.25 and 0.5 mph per year thereafter. That’s useful knowledge to plug into our expectations for the future, and we’ll also continue to get more robust data on aging curves with more years of information.

The point is, we’ve been looking at pitcher data to search for changes for quite a while. Raw pitch metrics provide useful feedback in that arena, and they’re often more quickly meaningful than outcome-based measures. The same is true for hitter data: We could already see how hard someone hit the ball, but that’s the output of a long chain of interconnected processes. Now we can measure the one that has to do with getting your muscles to move quickly and with force. That should help us understand hitter changes more quickly in the future.

2023 Standouts

Guess who swung the hardest in 2023? Giancarlo Stanton, obviously. But if you’re looking for more names than just the most obvious ones, here are a few. Junior Caminero’s average swing speed on balls in play was an absurd 80.2 mph in a tiny 23-swing sample. No surprise, then, that he was one of the biggest decliners in 2024 despite being one of the fastest swingers; it was just that small sample size evening out a bit. Want hope for the future? Nick Madrigal, swung faster and squared the ball up more frequently than Luis Arraez did, giving hope that he can be a similar type of player in the future. Did he stink up the joint in 2024? Sure. But he barely played and then broke his hand, so maybe 2025 will give him a chance to return to form. It’ll be easy enough to tell from the data!

Want to see what peak performance looks like? As he put a bow on his MVP season, Acuña generated top-10 bat speed and a best-in-league combination of squared up balls on fast swings. The next five on that list: Juan Soto, Aaron Judge, Iván Herrera, Carlos Correa, and Yordan Alvarez. There are some extreme Sesame Street vibes in that list – one of these hitters is not like the other – but it’s fascinating nonetheless to get a little more confirmation of what Acuña looks like at fully operational battle station levels.

Speaking of Acuña, his bat speed didn’t decline much in 2024, but his rate of “blasts” (that hard swing-squared up combination I mentioned up above) declined from 21.8% of swings to 12.7% of swings. In other words, he wasn’t getting the good contact he’d hoped for as much. Look at all the extra hard swings, even with the same average swing speed, from 2023:

Olson, on the other hand? His data from each season looked strikingly similar. How did he go from a torrid 185 wRC+ (his pace in the 2023 second half) to 117 in 2024? Clearly, bat speed isn’t the only thing that can explain how hitters change. But it’s at least good to learn that he’s not missing some physical ability that he had in his best year.

The Future

There’s a ton more research to be done, and I’m excited to have a bit of year-over-year swing speed framework developed before we start getting data from the new season. Context is everything, but putting these data into context promises to be exciting. Can you use bat speed changes to predict contact quality changes more quickly than before? Likely. Can you detect injuries and see which hitters have recovered to full strength more easily now? Almost certainly. Will we be able to tease out more about aging and predict which sluggers will stand up to the rigors of the season long into the future? I hope so. In any case, enjoy the new data, and let’s all get preemptively excited for the season all over again.