As you’ve probably seen by now, MLB rolled out some of their long-awaited bat tracking metrics Sunday night. There’s more to come throughout the year, but among other new statistics we received the bat speed of every pitch, “squared up” rate—which essentially measures how consistently a hitter makes flush contact—and most interestingly to me, swing length.
While bat speed is intuitive—and should track fairly closely with the exit velocities of a hitter—swing length is a nebulous area where we don’t have much prior research to fall back on. The vagaries of a bat path and the three-dimensional aspect of the zone are things commonly referenced but rarely elaborated on, and this is one of the first measures we’ve received that begins to pull back the curtain.
This is where I want to take a moment to talk about nomenclature. For most baseball fans, a “long” swing has oftentimes been a pejorative whenever talking about a hitter; you might hear a commentator say that Joey Gallo’s swing is long and therefore he misses a lot, for example. Meanwhile, the players lauded for being “pure” hitters all have short to the ball, sweet strokes. Think of your Michael Brantleys and Luis Arraezes, to name a couple. The contrast is clear: a short swing is good and desirable while a long swing is bad, difficult to control, and something of a mechanical cheat for generating power.
It’s no surprise, then, that some around the game began sounding alarm bells about players who seemed to rate poorly in both bat speed and swing length when these measures became public. Hitters like Nolan Arenado and Isaac Paredes stood out in comparison to their peers when their names showed up in the “longest swing” part of the leaderboards because of their slower bats:
At first glance, this leaderboard (laggardboard?) tracks with our priors; of course Javy Baez has a long, looping swing. And Giancarlo Stanton and Aaron Judge have always had more swing-and-miss to their games than 90% of the league, because they’re homer-focused slugging machines. But due to elite bat speed, plenty of these hitters were able to tap into enough power to make up for all those whiffs, so it all works out for them. The players that don’t have that dark red shading over their bat speed stick out like a sore thumb, though, and that’s where the concern stems from. A long, slow swing is one that seems on the precipice of a cliff, waiting to be exploited by pitchers with overpowering stuff.
But maybe it’s not all bad for these players. It’s important when a new statistic becomes available to look at the methodology so we can gain an understanding for what it is the metric is actually presenting to us. In this case, it’s not only showing us how long hitters’ swings are.
It’s also showing us where their swings are ending. Those are separate data points, but they’re both contributing to the swing length numbers we see on the leaderboards.
Which brings us back to Paredes and co. He, Arenado, Jose Altuve (and Jeimer Candelario) all have below-average bat speed and all show up inside the list of the 20 longest swings. Making the assumption that their swings haven’t dramatically changed since last season (since we only have bat tracking data for this season), we can say that all have been fairly successful power hitters over the last two seasons.
We also know that hitters who want to hit for power want to catch the ball in front of the plate; that’s how you muscle a ball out of the park when you don’t have the muscle of a Stanton or Judge. Taken in tandem, it seems likely that these players with slower bats are leveraging their other skills—pitch recognition, anticipation, and bat-to-ball ability—to “cheat” by trying to catch pitches far in front of the plate which they can pull down the line. In this way, it’s possible that the swing length metric we have now could be thought of as an approach measure alongside the mechanical traits inherent to a player’s swing.
To use one metric as an example of how this interaction of skills could work, all three of Paredes, Altuve, and Arenado were in the 78th percentile or better of SEAGER in 2023, suggesting their exceptional ability to identify incoming pitches allowed them to pull the trigger early enough to hit the ball out in front of the plate. (For whatever it’s worth, Paredes and Altuve are in the 71st and 74th percentiles of SEAGER this season, while Arenado fallen to the 45th percentile).
MLB has helpfully provided “bat_speed” and “swing_length” columns in their pitch-by-pitch data for games in 2024, which makes it possible to test the idea that length of swing as defined on Baseball Savant correlates to a hitter’s approach in where and how they want to hit the ball. Spoiler: It does.
This shows aggregated launch and spray angle—estimated based on hit coordinates—that’s been normalized for hitter handedness so that a negative number is a pulled ball for both left and right-handed hitters. What it shows is that the trajectory of a batted ball is clearly influenced by the length of the swing that produces it. Longer swings lead to pulled fly balls—but also pulled grounders, perhaps on mishits—and shorter swings often produce lower launch angles going the other way. These could be thought of as either defensive swings—when a hitter is beat—or the kind of soft line drive that a Luis Arraez or Steven Kwan excels at producing.
To isolate an estimate of a hitter’s contact point from the swing length we have, you could try to control for the hitter’s bat speed,which has a strong correlation with swing length, and the location of the pitch, since that also influences how much a hitter has to extend to make contact. The resulting difference between the estimated swing length and the actual swing length would theoretically represent how much their contact point adds or subtracts to their swing’s overall path.
It’s very rudimentary, but that’s what I did with the several weeks of swings we have so far (using a generalized additive model with random effects). And the results suggest maybe there’s some signal there:
The players whose names are shaded red hit the ball in front of the plate, making their swing “longer.” In some cases, by nearly a foot—Arenado adds more than 10” to his swing, according to this method. On the opposite end of the spectrum are players who shorten their swings by making contact much deeper in the zone. These players “let it travel.” The usual suspects are here (Luis Arraez, we see you) but we also see some frustrating sluggers who haven’t made the most of their ability this season. The way to interpret this is this: with their bat speed, these players should be making contact earlier than they are. This could be one reason why hitters like Jack Suwinski and Matt Chapman aren’t delivering as much thump in games as we expect them to.
To put a bow on things: Does this link between contact point and swing path mean we shouldn’t worry about hitters who don’t have great raw bat speed and do have “long” swings? Truthfully, it’s too early to tell one way or the other. But the mere presence of that combination doesn’t necessarily signal anything about an imminent decline from those players; it merely tells us they’re hitting the ball a different way from the other sluggers of the world. We intuitively suspected that was happening before, but now we have the numbers to back it up. That’s progress!
The long swing has long struggled against its reputation, and at first blush, MLB’s new metrics are unlikely to help. In the coming days, weeks, and months, I’m sure we’ll see plenty of research digging further into this shiny new data, and better modelers than myself will poke and prod the numbers until they produce additional insights. Even something as simple as the passage of time will bring additional swings, and those will be useful in helping us further our understanding of the game and the numbers.
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