What are the “torpedo bats” and why should you care?

A deep dive into the physics.

The big story to start this season is the “torpedo” or “bowling pin” bats which a handful of Yankees have used while hitting a ton of home runs. And it turns out that Giancarlo Stanton was actually using one last postseason when he slugged .709 with seven home runs. At least two Rays players, Junior Caminero and Yandy Diaz, have also begun experimenting with them.

Pioneered by Aaron Leonhardt, the one-time physics professor who became a Yankees minor league hitting instructor and who now works for the Marlins, these bats thin out the tip a little bit and move that thicker spot further down the barrel.

Jeff Passan wrote a good explanation of what the new bat is and where it’s come from. The inventors call them bowling pins instead of torpedoes, but admit the latter sounds better than the former.

The new bats could impact the game in at least three ways: physics, biomechanics, and vibes. Let’s dig into all three.

The Physics of the Bat-Ball Collision

I am not an MIT-educated physics PhD with seven years working as a physics professor, but I did take high school physics over two decades ago, so let me try to break this down. The most important concept here is that of the “sweet spot” of the bat, or the section where a hit will impart the most velocity to a batted ball. It generally sits four-to-six inches down from the tip of the bat, and what the torpedo design has done is to shift thickness from the end of the bat (which seldom produces hits) down towards that sweet spot.

The tricky question is: what does shifting the wood towards this point actually do to the bat dynamics?

I’ve found this paper by Dr. Alan Nathan, Characterizing the performance of baseball bats, to be most helpful to my understanding, but I also recommend:

• Performance versus moment of inertia of sporting implements by Cross and Nathan
• A comparative study of baseball bat performance by Nathan, Crisco, Greenwald, Russell, and Smith
• Daniel A. Russell’s explanation of the acoustics of baseball bats

The components that explain how fast a ball will come off the bat are:

1. Bat speed (very important)
2. Ball speed (much less important)
3. Effective rotational mass of bat (this is how figure the “Moment of Inertia” or MOI)
4. How efficiently kinetic energy is translated from the bat, to the ball as it compresses, and then into kinetic energy of the ball going the other direction. This is sometimes called the efficiency of the collision, or the “Coefficient of Restitution” (COR, and the NCAA uses the metric BBCOR). There are various statements of the efficiency of the energy transfer that are related but slightly different and we don’t need to go further into those weeds.

So shifting wood from the end of the bat towards the middle changes several of these factors.

A Lighter Bat

The bat becomes effectively lighter (although it weighs the same) because the mass of wood is less leveraged at the end — this is also why many bats scoop out the end, to decrease the rotational mass. In theory this would decrease the energy it has to impart, but that’s counteracted by the fact that a lighter bat is easier for the batter to accelerate. And according to Jeff Passan, all of the Yankees using the Torpedo bats are showing higher bat speeds than last year so far.

Among the five Yankees who have used the bat, all have seen bat-velocity increases year over year, with Volpe up more than 3 mph, Bellinger up 2.5, Wells 2, Chisholm 1.1 and Goldschmidt — an inveterate tinkerer who has also used bats with hockey-puck-shaped knobs — 0.3 mph.

One might assume that a lighter bat that a hitter can more easily accelerate is also easier to control and adjust in-swing, and that using a bat like this could improve bat-to-ball skills. In many ways this is simply a continuation of the trend where hitters are getting bats custom fitted to their swing and their own biomechanical levels, with the weight distributed in whatever way works best for them.

So while in theory there’s some decrease in the force of a swing from using a lighter bat like the torpedo, in the real world that’s probably fully overcome by the player being able to put that bat to faster and more precise use.

A More Efficient Transfer of Energy?

I started out thinking that the gain from the Torpedo bat came from increased stiffness, but that’s not the whole story. As Professor Russell alluded to today in this thread, energy is lost from the bat-to-ball collision when the bat vibrates, and how much the bat vibrates depends on whether the ball hits at or between these vibrational nodes, or resonances. This is why a ball in on the hands or at the end of the bat can break a bat — it’s landing at a point that causes increased vibrations.

The location of these resonant nodes aren’t purely caused by shape. The type of wood and the way the wood has been worked will have an impact as well, and we can’t say right now without further observation or laboratory testing whether the shape change has significantly moved the location of the sweet spot (it might have) or whether it’s sweetened the sweetness of the sweet spot (also possible).

What will be interesting to track though is Statcast’s Squared-Up metric. Squared-Up calculates the maximum exit velocity of a batted ball given the bat speed and the pitch speed, and then flags any batted ball that reached 80% of that MaxEV.

If the sweet spot has become sweeter on a torpedo, then players using them should see a bounce in their MaxEV that is not fully explainable by an increase in bat speed (hard to isolate if the torpedo also increases bat speed) and in their Squared-Up% that is not fully explainable by changes to launch angle, spray angle, and contact rate.

If the sweet spot has simply moved then the outcomes might be batter specific and harder to figure.

Who might the torpedo sink?

This is the part where we theorize wildly.

In our chat, Danny Russell (the DRaysBay editor, not the baseball physicist) wondered whether a massively strong hitter like Aaron Judge would lose exit velocity from the missing mass in a torpedo because he’s able to accelerate and control a heavier bat at near the max that a human can already. This is plausible, but also interesting that the first batter to use one was Giancarlo Stanton, the only hitter swinging significantly harder than Judge. The two Rays currently linked to these bats, Yandy Diaz and Junior Caminero, are also among the strongest hitters in baseball. Separately, Danny further postulated that Judge might actually be a bad candidate for a torpedo bat due to his already existent plus-plus barrel control.

He also wondered whether there are bat dynamics that matter for hitters with a lot of bat whip, like Brandon Lowe. You can think of bat whip as depending on where the fulcrum in the lever is — for hitters that turn around a point just below their wrists, the bat travels a tighter circle than for hitters who have more of their arms in their swing. Does that difference of bat path create some extra elasticity in the bat that a stiffer bat would lose?

I don’t know. I also don’t know a way to systematically measure this type of swing.

The piece of data I most want is hitter hand position at the time of contact and until we get that it’ll be hard to connect this data to biomechanical swing differences.

What about contact quality?

Maybe the most obvious difference between a traditional bat and a torpedo is that the barrel is larger and the tip is smaller. Is it possible that the larger barrel will make it easier for players to make contact? Absolutely possible, and we should be on the lookout for contact improvements from torpedo users, but it will be hard to isolate contact improvements that come from the fatter barrel from those that come from better control of a lighter bat.

It’s almost as interesting to wonder whether there’s a change to the hits off the end of the bat. Those batted balls are already of low value, with much of the energy being lost to bat vibrations. Can the tapered end and smaller diameter push more of those foul rather than see them become weakly hit balls in play? Is there benefit to making weak contact even weaker?

Conclusion

I don’t think we know much about these bats yet, and I don’t think they’ve broken baseball, no matter how many home runs the Yankees hit off Nestor Cortes. They’re unlikely to be a revolutionary advancement that changes the game as we know it. But they are very clever, and it’s not surprising that they appeared just two years after MLB teams began working with bat tracking data and studying the bat-ball collision more precisely.

Baseball is a game of information, epistemological expansion, and innovation. Every new bit of information changes the way we think about the game and leads us to new solutions that seem obvious in retrospect but that fit to questions we’d never previously thought to ask.

It’s beautiful and I hope that baseball never/always changes.