It's been five weeks since Major League Baseball unveiled its first batch of bat tracking data. Meanwhile, we've learned that Giancarlo Stanton swings hard, Luis Arraez swings fast, and Juan Soto is a god walking among us unbound by the pesky laws of physics and body mechanics. We learned that Jose Altuve actually has the swing of a man twice his size, and that Oneil Cruz has the swing of a much smaller man. Mainly, though, we learned when and where hitters swing the most. This is my fourth article on bat tracking data, and in collecting data for the previous three, I always found myself stuck in one part of the process: controlling variables.
As baseball knowledge progressed from the time of Henry Chadwick to the time of Tom Tango, we began to find better, more descriptive ways of measuring results. We went from caring about batting average to caring about OPS. We've found better ways to measure the small effects that add up to the big ones, from ERA to FIP and from OPS to wRC+. Then we entered the program after those results. We've moved on to strikeout rates and whiff rates, as well as average fly balls and ground balls. With the advent of Statcast, we were able to go deeper than ever into the process. We can look at the physical characteristics of a voice, just one voice, and show how well it will work. Within a given sample size, we can look at a rookie's most hit ball, just that one ball, and predict his future wRC+ more accurately than we can look at wRC+ throughout his rookie season.
Similarly, when I looked at average swing velocity and exit velocity from the first week of bat tracking, I found that swing velocity was highly 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 choose bad pitches to hit. Between 2015 and 2023, our database lists 511 professional strikers. I measured the correlation between their average exit velocity and their wRC+ during that time. R = .63 and R-squared = .40. But because tracking the bat takes us one step away from results and into process, it also separates from overall success. The day after the bat speed data was first released, Ben Clemens ran the correlation coefficients between all the success metrics. He found a .11 correlation between average swing speed and wRC+. Now that we have more data, I ran the numbers again and found that the correlation increased to .25. That's a big difference, but at the same time, the correlation between wRC+ and average exit velocity is .47.
If you want to know how hard a batter swings, you will find that it depends on the count, the type of pitch, the speed of the pitch, the location of the pitch, the depth of the contact, and whether the contact is made. at all. As a result, if you want to measure any effect of one factor on swing speed, you need to control for that, many others. The more I sifted through the details, the more I realized the old saying that pitchers control the action. Bat tracking shows us how right people are when they say hitting works. It shows us that different pitches require different swings.
When Tess Taruskin started putting together her Visual Scouting Primer series, she asked for scouting words and concepts that people had trouble picturing. Barrel diversity was high on my list. I know Eric Longenhagen makes a big point when he says that a player can move his barrel all over the place, but I've always had a hard time picturing that. Maybe it's because of the way I played the game when I was younger, but I never understood the concept of a strong swing. While digging into the bat tracking data, I see the effect of pitch type, location, and where in the space the batter has to find the barrel to make solid contact, ending up with a click.
Obviously there's a reason every hitter has a book, a certain way pitchers try to get it out. I'm not sure I've ever made such a clear connection to the physical action of swing, flexibility, quickness, strength, and overall athleticism required to execute a competitive swing on different types of pitches in different areas. And that's before we even get to the processing speed, judgment, and reaction time that comes with seeing a pitch and deciding not just whether to swing, but how to attack the ball. Tracking the bat highlights the path.
There are a million ways to be successful at the plate. Derek Jeter used an inside-out swing to send the ball the other way. Isaac Paredes uses the inside swing even more, reaching and hooking everything he can at the line. Chas McCormick and Austin Riley alternate to drive the fastball to the right field and pull anything slow to left. Arraez, like Tony Gwynn before him, sits back and puts the ball where he likes to put it. Ted Williams preached a slightly higher swing, making him the ancestor of today's Doug Latta students, who try to get on the plane with the ball early and meet it earlier, when their bat is on its way up. Some players talk about trying to hit the bottom of the ball to create backspin and carry. I could go on and on. But no matter which school of thinkers they enroll in, they don't decide what kind of voice comes next. Bat tracking data shows us how much their swing should change. Here's a map of the 13 game day positions, broken down by the average competitive swing speed at each position for right-handed hitters.
A hitter can bend at the waist and drop his bat head with a low pitch, especially on the inside. A high pitch requires a low swing, and it's more about pure spin speed. An outside pitch requires hitting the ball deep, where the bat may not be at full speed, but it also allows the batsman to stretch his arms. I just described three different skills, and there are many more that we can go into. Because every batter is an individual, each one will be better or worse at some than others.
In that moment when all of this clicked, I thought of Shohei Ohtani. Ohtani hits a bunch of balls that are obviously gone from the second he makes contact. But he also hits some of the strangest home runs you can imagine, swings that end up moving the body in a strange way that makes it seem impossible that he was able to hit the ball hard. It looks like he's stepping to the bucket and spinning the ball, he looks like he's throwing his belt to attack the outfield, or he looks like he's not swinging too much, but the ball ends up on the fence. . Somehow this ball left the bat at 106.4 mph and traveled 406 feet.
It may seem that this habit was above the body. However, swinging is like cracking a whip, where you work from the bottom up to send all the power to the end of the line. Some hitters are better than others at controlling their bodies to fully transfer power. Here's another way to look at this.
On the left are the 26 homers hit by Cody Bellinger in 2023. At right are Ohtani's 44 homers. I note that because Ohtani has hit 18 more, his chart looks very strong. But it's not just about the number of dots. It's about spreading. I'm not trying to pick on Bellinger. I used him partly because he had a good season. I found his pitch chart by looking for players with the highest home run percentage in the middle of the strike zone. At 46%, Bellinger had the highest 20 home run rate of any player. If you make a mistake in the middle, you will destroy it. Ohtani, on the other hand, can hit the ball hard almost anywhere. It's even clearer if you look at the heat maps of the two players on hard-hit balls last season.
Bellinger hasn't been the same player since his 2019 MVP campaign, and it's generally assumed that the injuries that followed affected his swing. You can still do a lot of damage, but in smaller subsets. This is one of the reasons scouts focus so much on swing and run and take the time to define a prospect's swing as swing or swing, long or short, swing or not, overhand or underhand. 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 out of not just the A-swing, but a swing that can hit any pitch that comes their way.
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