The 2025 Major League Baseball season certainly started with a bang—at least for the New York Yankees. At Yankee Stadium against the Milwaukee Brewers, the Bronx Bombers blasted an MLB-record 15 home runs in the first three games, including nine homers in a 20-9 bludgeoning of the Brewers in the second game of the series, and another four for good measure the following day.

Those were attention-grabbing numbers. But what set baseball fans abuzz was the oddly shaped bats used by several of the Yankees—“bowling pin” or “torpedo” bats that were fat at the “sweet spot” and tapered at the end.

The design is the brainchild of Miami Marlins field coordinator Aaron Leanhardt, a former MIT physicist. And, yes, the bats are legal and approved for use by MLB. The rule is: “The bat shall be a smooth, round stick not more than 2.61 inches in diameter at the thickest part and not more than 42 inches in length. The bat shall be one piece of solid wood.”

But could the barrage of home runs be attributed to these oddball bats?

The maximum diameter and the length of a torpedo bat are equal to the dimensions of a standard bat. Credit: Zeamays, Wikipedia Creative Commons.

Amid all the speculation and my own angst as a Brewers fan (full disclosure), I set out in search of the facts. I’m fortunate to have found a reputable source of bat performance in Dr. Lloyd Smith, director of the Sports Science Laboratory (SSL) at Washington State University, specializing in the dynamics of bat and ball collisions. Smith has been doing this research for decades, is a widely acknowledged expert in the field, and the embodiment of the quality bromide, “You get what you measure.”

Among the things measured in Smith’s lab are:
• The mass moment of inertia (MOI), a measure of the distribution of mass in the bat. A knob and end-loaded bat may weigh the same, for instance, but the end-loaded bat will have a higher MOI. Bat speed depends on MOI, and is an important component of laboratory performance tests.
• Swing speed refers to the effect that bat weight (or MOI) has on the speed a bat may be swung in play. It plays an important role in determining bat performance and must be found empirically.
• The bat performance test measures the bat and ball speeds before and after impact in a controlled laboratory setting.

And if you delve further into the SSL site, you’ll find data sufficient to satisfy those of you who are mathematicians and physicists. I am neither of those, so I had questions.

There are a lot of descriptions of these torpedo bats or bowling pin bats. How would you describe or define these bats?

“Torpedo bat” certainly sounds cool, but I think “bowling pin bat” is probably a more accurate description. When I’m trying to describe it over the phone, I just tell people that a traditional bat has a bat or barrel diameter that increases uniformly all the way to the end of the bat.

With a torpedo bat, the diameter increases up to the sweet spot, and then it decreases. That’s really the difference. The torpedo bat’s barrel diameter decreases to the end of the bat, whereas with the traditional bat the diameter stays the same, or actually increases a little bit, beyond the sweet spot.

One description I read is that the torpedo bat redistributes the weight to a spot 4 to 6 inches away from the end of the bat. That seems a little long, but I suppose the taper might go that far from the end of the bat.

Yeah, well, the sweet spot of the bat very often is around 6 inches from the end. That’s the location that you’re trying to get, and that’s the motivation of the torpedo bat, to get the diameter of the bat at that location as high as you can. That’s really the argument for it.

The interesting thing is that with a traditional bat, where the diameter could be increasing beyond the sweet spot, you think about it and that’s got to be the dumbest idea in the world. Why would you want the end of the bat to be big? You really want the sweet spot of the bat to be big, if, for no other reason, it gives you just a little bit more hitting surface and maybe a little more chance to be fouling the ball off.

Right, if you’re hitting it off the end of the bat, you’re not getting a hit anyway.

Exactly, it’s gonna be a poor hit anyway, it’s doing very little for you. So for 150 years, people really didn’t think or realize they’re putting a lot of weight in the bat and not putting it at the proper location.

So, about that sweet spot. If it’s possible to move it, is it possible to make it bigger or somehow sweeter?

Well, sweeter is a different question, but let’s talk about making the barrel bigger. Wood bats are heavy, and people do all they can to make them lighter. One way of doing that is reducing the diameter of the bat. The barrel is allowed to be 2 5/8 in. diameter, and most bats don’t have that at the sweet spot. So one clear advantage of the torpedo shape is that it allows you to maximize the barrel diameter to the limit at the sweet spot, which is cool.

Now, you asked, does it make the bat sweeter? And I think by that you were asking can it actually hit the ball farther then you would have with a bat that does not have the torpedo shape. And so far we have no evidence of that, and I don’t think that there is.

Would your average be a little bit higher with the torpedo bat because your barrel is a little bit larger in diameter at the sweet spot? Yeah, probably. But would you hit more home runs with the torpedo bat than with a traditional bat. No.

In the various tests, what does the math indicate? Is the inertia test the most important? Which tests show the biggest difference between the torpedo shape vs. the traditional shape?

Well, I’ll wax a little philosophical here. I would say the inertia test is one of the most overlooked tests in all the bat kingdom. [Laughs.]

For whatever reason, all bats, amateur, hollow bats, and wood professional bats, we talk about drop weight. And that’s gonna be the difference between the length of the bat in inches and it’s weight in ounces. We just use that term. A minus 3 is going to be the desired drop rate for a wood bat, and when we get into hollow bats [such as aluminum bats], then typically a minus 5 or 6 for a heavy bat, and then super-light bats are minus 10, and some even minus 12.

A number of people have tried to promote the idea of swing weight, which would be the MOI, but it’s never caught on. So we always go back to this drop weight. So, for sure, I would say that the inertia or MOI of the bat is an underrated property that should get more attention.

I’ve seen various theories that if people do better with it maybe it’s just a matter of bat speed, because it’s easier to swing. Is that the same idea as the end of the bat being hollowed out?

Yes, if you cup the end of the bat it’s similar for the weight properties, it’s similar to having a bowling pin shape for the bat. But we have to be careful when we talk about benefits, getting a higher swing speed because you reduce the weight of the bat. That’s something that people will often say, but it’s not actually correct. We do know that if you reduce the weight of the bat, your swing speed is going to increase. That happens for sure. And you can do that by corking the bat, you can do that by cupping the bat, or you can do that with a torpedo or a bowling pin bat. All of those can lower the swing weight of your bat and increase your swing speed.

The problem is that when you do that, you now have less inertia on the bat. There’s less mass there. And as you reduce the mass, that lowers your batted ball speed. So, when you change the weight of the bat, there is now a competition. If you lower the weight and increase the swing speed, which is going to have more of an effect on your batted ball speed—the penalty from the reduced weight, or the benefit from the increased speed? It’s not something we can predict. We don’t know because it depends on how the muscles in your body respond to the changes in weight.

Bat testing cannon with Dr. Lloyd Smith (right) and Nate Griggs. Credit: WSU

So we have to measure that, and it turns out we’ve done a lot of those measurements. We measure the effect of bat inertia on swing speed. And it turns out that in that competition between reduced weight and greater swing speed, your batted ball speed goes down as you reduce the weight of the bat. So if your goal in life is only to increase batted ball speed, you actually want to be adding weight to the bat, not reducing the weight.

And this has to do with MOI, the “moment of inertia.”

Exactly. That’s exactly the right term. Your swing weight is quantified and measured using what we call the mass moment of inertia, or the MOI of the bat.

Do the characteristics or the qualities of the wood or the wood grain play a part at all?

Not so much. When a batter picks out a wood bat, they always want to have nice clean, straight grain. That has more to do with the strength and durability of the bat than its performance. If you have just horrible wood with all kinds of knots and junk in it, yeah, that’s a problem. But if you look at two bats and one bat has nice, straight, clean grain, and another bat has grain that’s out of line or angled, the performance is going to be pretty similar. But the straighter grain is going to have a higher strength, it’s going to last longer and be able to take an inside hit better than the other bat.

I just thought perhaps the taper would interrupt the grain as opposed to that long, straight grain...

Right, but the barrel is not the part of the bat that breaks. It’s usually going to be in the taper [down by the handle], and the taper of a torpedo bat and a traditional bat is quite similar.

Babe Ruth used a bat that was 36 in. long and weighed 44.5 oz. I suppose on one hand, that would give a ball more inertia, but I think actually you just have to be Babe Ruth.

Exactly. It is so impressive that he was such a good batter with that big of a bat. And the other part of that is that it’s not easy to make that ball contact. If your only goal is to hit the ball far, then you want a heavy bat. But you also have to make that bat and ball come together in the right way, and that’s the other reason to want a lightweight bat, just to be able to get on base, to get that ball in play. It’s so impressive that Ruth was able to be such a good hitter [714 career home runs] and have that batting average [.342 lifetime] with such a heavy instrument.

A National Baseball Hall of Fame traveling exhibit featured (from left to right) bats used to hit: Babe Ruth’s 60th home run in 1927; Roger Maris’ 61st in 1961; Mark McGwire’s 70th and Sammy Sosa’s 66th in 1998. Credit: Anetode at English Wikipedia.

You mentioned the MOI test. What are the other tests that closely relate to trying to figure out what these bats are doing or not doing?

The inertia is one, measuring what the swing weight is, but the other one is going to be measuring performance directly, where we can then say how much energy is lost in the impact.

And that’s what my lab specializes in. We do that for every amateur bat that’s used in play, from youth to adult baseball and softball. Through a lot of this work we understand that process really well. And we actually have plans this summer to do that same testing for torpedo bats.

We did one quickly. We took a regular bat to our machine shop and had them machine it down into a torpedo bat shape. And that gave us a little bit of an idea. One of the arguments that people have made about a torpedo bat is that you can move the sweet spot. And that was the justification that the Yankees gave, that one of the batters was hitting the ball too far inside. And so they said, let’s see if we can get this torpedo bat and move the sweet spot inside, and his hitting will improve.

And so, on the one test that we quickly did, we were able to show that. We measured the performance of the bat before we cut it into torpedo shape, and then we measured it with the torpedo shape, and the sweet spot did move. Interestingly, the sweet spot did not move as much as that bowl, that largest diameter part of the bat, moved. So it’s not as if it’s as simple as to say, well, the sweet spot of the bat normally would be 6 inches in from the end, I want it to be 8 inches in from the end so then we’ll move that bowl back to 8 inches. You’d have to move it more than 8 inches to get your sweet spot.

So, there’s quite a bit of subtlety and nuance that goes into tailoring these torpedo bats. And while some people are trying to make the bat lighter, some people aren’t. Some people are fine with the swing weight of the bat. They just want to have a little larger hitting area at the sweet spot, and some torpedo bats are made that way.

That’s interesting because if you could customize a bat to better suit a particular player, that’s a whole science that I’ve never heard anything about.

Yeah, it’s neat, that’s one of the more interesting things because there’s another way to move the sweet spot in, and that’s just by swinging a shorter bat. [Laughs.] I have not heard anybody explain why you would want to go to the effort of making a torpedo bat for a particular player rather than just giving him a shorter bat to swing. I haven’t heard that explanation. But they’re smart people. I’m sure there’s a reason out there, but it’s not one that’s been disclosed to me.

When I first got into this business, it was very apparent that in many bats, there are things that were promoted as being significant in contributing to bat and ball speed that were absolutely not true. I used to look at those things and say, “Well, that’s nonsense, and why would anyone want to swing like that?”

But at the end of the day, games are won and lost by the margins, by the smallest of margins. And if a player thinks they have a better product, that’s going to give them confidence that they would not otherwise have. And very often, games are won by your mental condition. How are you emotionally in your space? If bat design or color or shape in a certain way gives you better feeling, maybe that could be just enough to help. So, even if this stuff with the torpedo bats is psychological, that’s still a benefit.

“Baseball is 90% mental. The other half is physical.”—Yogi Berra