﻿ The Physics of Choking Up | The Hardball Times

# The Physics of Choking Up

Joey Votto is among the best hitters who chokes up on the bat. (via Hayden Schiff)

Editor’s Note: Please also read this FanGraphs piece by Eno Sarris, which was written in conjunction with David’s.

Have you ever swung a bat by the barrel end? Go ahead. Give it a try. I’ll wait. You should notice that it is dramatically easier to swing the bat from the barrel end than the handle end. In general, it is easier to rotate an object that has more of its mass near the axis of rotation than an object that has more of its mass further from the axis.

The “rotational inertia” of an object is a measure of how hard it is to get the object to rotate. Objects that have a large rotational inertia have proportionally more of their mass farther from the axis of rotation than objects that have more of their mass closer to the axis. In other words, if you swing a bat by the barrel end, it has less rotational inertia than when you swing it by the handle end.

If batters can get the bat into the hitting zone as fast as possible, they can wait as long as possible to decide whether to swing and where to expect the ball. If that is their goal, then they should hold the bat by the barrel end. I suspect you’ve already realized that if a batter swung the bat by the barrel against a big-league fastball, the handle would snap like a twig.

Clearly, batters aren’t interested just in getting the bat into the hitting zone quickly. They are also interested in getting as much lumber as possible on the ball. This is the “great compromise” for hitters. They must find the right combination of a quick swing versus putting “good wood on the ball” that will maximize their paycheck. Batters who tend toward the quick swing sometimes choke up, while power hitters focus on the big stick.

If batters want to get their bats into the hitting zone more quickly, a physicist would tell them to reduce the rotational inertia of the bat, making it easier to rotate the bat more quickly. That is, the batter must get a greater fraction of the bat closer to the axis of rotation or equivalently have less of the bat further away from the axis.

The sketch below illustrates two ways to accomplish this goal. In the left-most image, there is a bat swung around the red dot near the handle end. Notice the fraction of the bat outside the red circle. It might be around 80 percent of the bat’s total mass.

The middle picture shows the bat rotating about a red dot further up the handle as if the batter is choking up. Now, only about 60 percent of the bat is outside the circle. Since there is less of the bat further from the axis, the rotational inertia is smaller and the bat can be sped up more rapidly.

The right-most image shows a smaller bat being swung around the red dot back near the handle end. If you look carefully, you’ll notice the red circle goes a bit farther up the bat than the red circle in the left-most image. So, swinging a shorter bat is somewhat equivalent to choking up.

Why would a batter choose to choke up instead of just using a shorter bat? Great question — I’m so glad you asked. A shorter bat probably weighs less, making it somewhat less effective. On the other hand, the average speed of a choked-up bat is smaller. More on this in a bit.

Both reasons result in somewhat less effective ball-bat contact. So, I suspect the reason that hitters choke up instead of going with less bat has to do with situational hitting. With the count in your favor late in a close game you might risk not choking up to put a serious charge into a ball. On the other extreme, if you are behind in the count, choking up might be the way to go, just to put the ball in play. The point is, it is bad form to call timeout to change bats.

Perhaps you have already realized that you can make the bat easier to swing and quicker to the hitting zone by simply choosing a lighter bat of the same length or, dare I mention it Sammy, hollow out the center of the barrel. These methods do make the bat faster, but less effective because it is now lighter.

So, is any of this real? A 2010 research paper in The Sport Journal reports the following results comparing the swings of batters with and without choking up. The authors state:

1. The choke-up grip had significantly less swing time and stride time than the normal grip.
2. The choke-up grip had significantly greater bat tip velocity than the normal grip.
3. No significant difference between choke-up and normal grips in bat-ball accuracy.

Items one and two make sense because the lower rotational inertia of the bat allows the hitter to speed the bat up more easily. Item three is a bit disturbing. After all, the purpose of choking up is to increase the likelihood of solid contact. I’m not going to worry too much about it because the batters were hitting off a pitching machine with speeds around 75 miles per hour – not near major league game conditions.

A Hardball Times Update
Goodbye for now.

Now that I think about it, item two is also kind of funny. If choking up results in faster bat tip speeds, why do hitters who choke up sacrifice power for contact? I suspect this is due to the distinction between the speed of the tip of the bat and the average speed of the entire bat.

The physics of the ball-bat collision tells us that the effectiveness of the bat depends on the mass of the bat and the average speed of the entire bat (usually called the “center-of-mass speed”). The motion of a bat moving to the hitting zone is complex, but it can be thought of as a combination of the forward motion of the bat toward the pitcher plus the rotational motion of the bat we mentioned earlier.

The complex motion of the hands as a whole is a portion of the motion of the bat. In addition, as batters go through their swing their dominant hand (right hand for a righty) starts farther from the pitcher than their non-dominant hand (left for a righty). As the bat reaches the hitting zones the two hands are about equidistant from the pitcher. During the follow-through the dominant hand is now closer to the pitcher.

My point is, a portion of the bat’s motion involves rotation about a point between the two hands during the swing. Looking at a normal grip, the batter’s hands are going through their complicated motion while at the same time the bat is in rotation about a point near the knob end.

For choked-up grips, the hands are also moving, but the bat is now rotating about a point further up the bat. Just looking at this rotational motion, the knob end of the bat is actually rotating away from the pitcher. This results in the average forward speed of the bat being lower as mentioned earlier. Below is a sketch designed to help understand this difference in average total speed.

The bat on the left has a normal grip near the knob, while the bat on the right is choked up. Considering only the rotation of the bats, each is broken up into five sections of roughly equal mass by the black dashed lines. For each section the speed of the bat is shown.

These are round numbers to illustrate the issue and not to be taken too seriously. I picked them so averaging would be relatively easy, not because they are correct for some particular batter’s swing. It should also be noted that, in addition to the rotation of the bat, the hitter’s hands are also moving forward toward the pitcher. I have ignored this piece of the motion for clarity and because it is very similar for both grips.

The choked-up bat has a higher tip speed than the normal grip. The rest of the speeds were estimated by using the “merry-go-round rule.” The horse near the outside edge is going twice as fast as the horse only half-way to the outside edge. The speed of each portion of the bat is linearly proportional to the distance from axis of rotation — the red dot — roughly the spot between the batter’s hands.

According to the data we looked at, the tip speed of the choked-up bat is higher that the tip speed for the normal grip. Note the speed of the bat just due to the rotation must be zero where the hands grip the bat. These two conditions require the speeds to drop faster for the choked-up grip compared to the normal method. Also notice the knob of the choked-up bat is indeed moving backwards as mentioned earlier.

For each grip, we just need to average to five speeds on each bat to get the average speed. For the normal grip the result is 50 mph, while the choked-up bat has an average speed of 45 mph. So, we see that the speed of the tip of a choked-up bat can be higher and the average speed be lower. Since the average speed of the bat determines the exit speed of the ball, choking up indeed sacrifices power hopefully in exchange for a higher probability of contact.

I hope this explains some of the physics of choking up. If not, I guess I’m the one that choked up.

### References & Resources

David Kagan is a physics professor at CSU Chico, and the self-proclaimed "Einstein of the National Pastime." Visit his website, Major League Physics, and follow him on Twitter @DrBaseballPhD.
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yojiveself
6 years ago

just wanted to say this was a fascinating read. good job!

David S
6 years ago

” choking up might be the way to go, just to put the ball in play. The point is, it is bad form to call timeout to change bats.” I think also you have to factor in changing weights of bats during an at bat. Not being used to the bat you changed to all the time; might itself put you at a slight disadvantage. Just a thought. Like throwing balls at differing weights would be different for your anatomy. Our hardball coaches always told us during the season. Do not play or throw a softball-it will screw up your arm.

jim
6 years ago

Have you done something like this with the ax bat when compared to the normal bat style?

MetsMind
6 years ago

Interesting article. I almost never see anyone choke up on the bat now-a-days. In fact, more players try to extend a pinky finger off the end of the knob. A reverse choke, I guess you could call it. Imagine someone like Felix Milan, Mets second baseman from the 70s trying to break into the big leagues today. He’d never be allowed past AA.

87 Cards
6 years ago

The Big Cat led the NL in ABs/Ks in 1971, 1973, 1974 and 1975. High-contact and his good -glove helped him rise to MLB/Japan. If only Charlie Lau had gotten a chance to tinker his swing for his high contact eye …….

Michael Bacon
6 years ago

I believe you are referring to former Braves second baseman Felix Milan. I’ve tried to imagine little Felix trying to break into the big leagues today…He is listed as 5-11, 172 lbs. Considering how much larger are the players of today, you may be right about him but because of his fielding ability, he would play in AAA, at least.

Andrew Perpetua
6 years ago

Coming from a fencing background, I find myself wondering why baseball has shied away from the split handed grip. It seems to me it would offer benefits from both the choked up bat and the standard grip. Your top hand is further up the handle, so you have more leverage to get the bat moving, then by the time the bat goes through the zone your hands are together as if you were using a standard grip.

I’m curious if you have tested for this sort of thing? Or if anyone has? I guess it would be difficult to test since I’m not sure a single elite level baseball player uses such a grip. Although that hasn’t always been the case.

Michael Bacon
6 years ago

Ty Cobb tested the split handed grip over a century ago and the results were phenomenal.

Greg
6 years ago

If you look at stills of Cobb at or near striking the ball, his hands are together. He seems to have started with them apart, as an axe swinger might, with the top hand sliding down during the swing.

David Kagan
6 years ago

It has been pointed out to me that the article I referenced says the opposite of what I claimed. The statement from the article is “Results also indicated significant greater bat velocities (p = 0.01) with normal grip swings than the choke-up grip swings. “

I supposed in our current cultural climate, I should say something about “alternative facts.” However, this is science and this is exactly how science works. A scientist shares theories and data with the community for the express purpose of testing whether the science withstands the debate that ensues.

This process is designed to weed out errors and charlatans. I hope I have a track record that indicates the former not the latter. In any case, the result of the debate is always better science. Thanks for pointing out my error.

As far as correcting the science in the article, if the bat is actually moving more slowly with a choked-up grip, then the ball will come off it more slowly. No complex explanation required.

Beep Boop
6 years ago

Dr. Kagan,

I’m reading through the DeRenne et. al. paper, and I can’t find any mention of “The choke-up grip had significantly greater bat tip velocity than the normal grip.”

In fact, Table 1 and the Results section state exact opposite, “mean normal grip swing 3.0 m/s (10%) faster than the choke-up grip swing.”

The apparent paradox of the results comes from the fact that choking up results in a quicker time from stride to contact, despite a slower bat speed. The data shows that choked up grips result in roughly equal time improvements in both the “stride” and “acceleration” phase of the swing for a choked up bat. The acceleration could be explained by the reduction in rotational inertia, which would result in a quicker acceleration of the bat for the same torque. The stride improvement indicates that the batters are changing their approach in ways that goes beyond simple hand placement on the bat.

On a choked up bat, the tip has a lower translational velocity for the same omega (it’s hard to imagine that a batter could produce a significantly higher rotational velocity just by cheating a couple inches), due to the smaller radius. Although your explanation of “faster tip, but slower CM” makes logical sense, the mass distribution of the bat makes it such that the influence of the barrel portion of the bat is much larger than the grip. I suspect that if we actually integrated the momentum of the bat slivers from knob to tip, the results of your simplified example would look much different.

ckdu
6 years ago

KIDNEY DIALYSIS: what happens if you end it? http://kidneyok.tumblr.com/

Sticki
6 years ago

Interesting article but I think the -25 mph when below the hands on the choked up grip actually has a positive effect on the bat above the hands and should actually have been added to the average as a reverse -25 mph which in essence is a +25 mph which would make the average speed on the choked up grip 55 mph and faster than the regular grip.

Greg
6 years ago

One missing thing – what about just using a shorter bat? If indeed the velocity of the knob end below the hands takes away from average velocity (disputed in another comment), then a shorter bat held at the end would seem to give greater average velocity.

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