It’s been five weeks since Major League Baseball unveiled its first trove of bat tracking data. In that time, we’ve learned that Giancarlo Stanton swings hard, Luis Arraez swings quickly, and Juan Soto is a god who walks among us unbound by the irksome laws of physics and physiology. We’ve learned that Jose Altuve really does have the swing of a man twice his size, and that Oneil Cruz has the swing of a slightly less enormous man. Mostly, though, we’ve learned when and where batters swing their hardest. This is my fourth article about bat tracking data, and in gathering data for the previous three, I constantly found myself stuck in one particular part of the process: controlling for variables.
As baseball knowledge has advanced from the time of Henry Chadwick to the time of Tom Tango, we first found better, more descriptive ways to measure results. We went from caring about batting average to caring about OPS. We found better ways to weight the smaller results that add up to big ones, going from ERA to FIP and from OPS to wRC+. Then we got into the process behind those results. We moved to chase rates and whiff rates, and the ratio of fly balls to groundballs. With the advent of Statcast, we’ve been able to get deeper than ever into process. We can look at the physical characteristics of a pitch, just a single pitch, and model how well it will perform. Within a certain sample size, we can look at a rookie’s hardest-hit ball, just that one ball, and predict his future wRC+ more accurately than if we looked at the wRC+ from his entire rookie season.
Similarly, when I looked at average swing speed and exit velocity from the first week of bat tracking, I found that swing speed was more predictive of future exit velocity. Exit velocity is the result of several processes: You can’t hit the ball hard unless you swing hard and square the ball up, and you can’t square the ball up if you pick terrible pitches to hit. Between 2015 and 2023, our database lists 511 qualified batters. I measured the correlation between their average exit velocity and their wRC+ over that period. R = .63 and R-squared = .40. But because bat tracking takes us one more step away from results and toward process, it’s further divorced from overall success at the plate. The day after bat speed data was first released, Ben Clemens ran some correlation coefficients between some overall metrics of success. He found a correlation of .11 between average swing speed and wRC+. Now that we have more data, I re-ran the numbers and found that correlation has increased to .25. That’s a big difference, but over the same period, the correlation between wRC+ and average exit velocity is .47.
If you want to know how hard a batter is swinging, you’ll find that it’s dependent on the count, the type of pitch, the velocity of the pitch, the location of the pitch, the depth of contact, and whether contact takes place at all. As a result, if you want to measure any one factor’s effect on swing speed, you need to control for so, so many others. The more I’ve sorted through the data, the more I’ve come to appreciate the old adage that pitchers control the action. Bat tracking shows us just how right people are when they say that hitting is reactive. It shows us that different pitches essentially require different swings.
When Tess Taruskin started putting together her Visual Scouting Primer series, she asked around for scouting terms and concepts that people had a hard time picturing. Barrel variability was at the top of my list. I know that Eric Longenhagen is giving a glowing compliment when he says that a player can move his barrel all around the zone, but I’ve always had trouble picturing that. Maybe it’s because of the way I played the game when I was younger, but I’ve never really understood the concept of a grooved swing. When I was digging through the bat tracking data, seeing the effect of the pitch type, the location, and where in space the batter has to get the barrel in order to make solid contact, it finally clicked.
There’s obviously a reason that every hitter has a book, a certain way that pitchers try to get them out. I’m just not sure I ever connected it quite so clearly to the physical act of swinging, the flexibility, quickness, strength, and overall athleticism required to execute a competitive swing on different kinds of pitches in different locations. And that’s before we even get to the processing speed, judgment, and reaction time that comes with recognizing the pitch and deciding not just whether to swing, but how to attack the ball. Bat tracking highlights the how.
There are a million ways to succeed at the plate. Derek Jeter used an inside-out swing to send the ball the other way. Isaac Paredes uses an inside-even-further-inside swing, reaching out and hooking everything he can down the line. Chas McCormick and Austin Riley time their swings in order to drive a fastball to the right field gap and pull anything slower toward left. Arraez, like Tony Gwynn before him, stays back and places the ball in the exact spot that he feels like placing it. Ted Williams preached a slightly elevated swing, making him the progenitor of today’s Doug Latta disciples, who try to get on plane with the ball early and meet it out front, where their bat is on an upward trajectory. Some players talk about trying to hit the bottom of the ball in order to create backspin and carry. I could go on and on. But no matter what school of thought batters subscribe to, they’re not the ones who decide what kind of pitch is coming. Bat tracking data show us just how adaptable their swing has to be. Here’s a map of the 13 gameday zones, broken down by the average speed of competitive swings in each zone for right-handed batters.
The batter can bend at the waist and drop his bat head on a low pitch, especially inside. A high pitch requires a flatter swing, and it’s much more about pure rotational speed. An outside pitch requires hitting the ball deeper, where the bat might not have reached full speed yet, but it also allows the batter to get his arms extended. I just described three different skills, and there are plenty more that we could dive into. Because every batter is an individual, each will be better or worse at some of them than others.
At the moment when all this clicked, I thought of Shohei Ohtani. Ohtani hits plenty of balls that are very obviously gone from the second he makes contact. But he also hits some of the most awkward home runs imaginable, swings that end up with his body contorted in some weird way that makes it seem impossible that he managed to hit the ball hard. He looks like he’s stepping in the bucket and spinning off the ball, he looks like he’s simply throwing out his bat to foul off an outside pitch, or he looks like he’s just not swinging very hard, and yet the ball ends up over the fence. Somehow this ball left the bat at 106.4 mph and traveled 406 feet.
It might appear that this swing was all upper body. However, a swing is a little bit like cracking a whip, where you’re working from the bottom up to send all of the energy to the very end of the line. Some hitters are better than others at manipulating their bodies to time that energy transfer perfectly. Here’s another way of looking at this.
On the left are the 26 homers that Cody Bellinger hit in 2023. On the right are Ohtani’s 44 homers. I realize that because Ohtani hit 18 more, his chart looks more robust. But it’s not just about the number of dots. It’s about the spread. I’m not trying to pick on Bellinger. I used him in part because he had a great season. I found his pitch chart by searching for players with the highest percentage of home runs in the very middle of the strike zone. At 46%, Bellinger had the highest rate of anyone who hit 20 home runs. If you make a mistake in the middle of the zone, he’ll destroy it. On the other hand, Ohtani is capable of hitting the ball hard just about anywhere. It’s even clearer if you look at the two players’ heat maps on hard-hit balls from last season.
Bellinger has never been the same player since his 2019 MVP campaign, and it’s generally assumed that the significant injuries that followed affected his swing. He can still do major damage, but on a smaller subset of pitches. This is one of the reasons that scouts focus so much on flexibility and athleticism and take the time to describe the swings of prospects as grooved or adaptable, long or short, rotational or not, top-hand or bottom-hand dominant. These things may not matter much in batting practice, but if there’s any kind of pitch you can’t handle, the game will find it. The best hitters find a way to get off not just their A-swing, but a swing that can succeed against whatever pitch is heading toward them.
