A pitching model: playing the slots

Any fan of baseball knows something about arm slots (also known as “arm angle”). We’ve all seen the industry standard, high ¾ delivery of countless pitchers. We’ve also seen the oddballs: the sidearmers and submariners. You’ve also probably noticed that the ball does weird things when they throw it. Mostly they all have sinking fastballs, but you may have also heard oddities like rising sliders and other strangeness. This may surprise you, but Chad Bradford and Brad Ziegler don’t hold the ball any differently than any conventional pitcher. The only difference is their arm slot.

But before we get too far into that topic, we need to understand how different pitches are spinning the ball and what kinds of pitches result. As in my other articles, it is instructive to create a somewhat artificial construction to help visualize what is going on. Let us consider a pitcher who throws perfectly overhand. His arm slot is perfectly perpendicular to the ground when he throws. There are pitchers with very high arm slots such as Hideki Okajima, a relief pitcher with the Red Sox. High arm slots are reputed to provide more velocity, less lateral movement, and short careers due to extra strain on the shoulder. I don’t have any easy explanations for the velocity boost nor the mistreated shoulder, but I can shed some light on why these guys have a reputation for less movement.

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Here’s a typical Okajima delivery. He is one of the most extreme overhand pitcher in the major leagues. And Yes, he’s not looking where he throws when he pitches.

Let’s look at how a standard fastball would look from a right-handed extreme overhand pitcher from the batter’s perspective. Because the arm slot is perpendicular to the ground, a fastball, with the most efficient “inline” spin has a spin axis perfectly parallel to the ground and perpendicular to the arm slot.

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Notice how it has pure backspin. That is, pure hop with no tailing or boring movement whatsoever: a straight pitch.

Now let’s look at an overhand curve—the opposite of a fastball—from the same pitcher and the same point of view.

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Notice how this pitch is also perfectly aligned except the spin is all topspin. This pitch is also straight, but where the fastball hops, it dives into the dirt.
There you go. Two bread and butter pitches that an overhand pitcher could throw and neither moves in the horizontal plane. Their reputation of lacking movement is definitely deserved.

Let’s move onto our next hypothetical pitcher: the perfect sidearmer. Sidearmers have a reputation for less velocity, a lot of lateral movement, and a more shoulder friendly delivery. In fact, as Pedro Martinez’s shoulder gets more and more damaged the lower his arm slot gets. But once again, I can only shed light on the side to side movement that is observed.

Here’s the fastball from a right-handed sidearm pitcher from the batter’s point of view.

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Pretty weird, I know. There’s no backspin at all. Is that even a fastball? It’s held like one, for sure. All that has happened is that the arm slot has tilted 90 degrees so the spin axis also tilts 90 degrees. What you end up with is a fastball with tons of action and tons of sink since there is no backspin to give it any hop.

You probably have a good idea what the curveball looks like, but here it is anyway.

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Now we end up with a curve with no down-bite. It still has the speed of a curve and will get some drop by virtue of gravity, but all the movement induced by the spin is to the side. It will have a lot of sweeping movement away from a same handed batter. The point of all this is to establish the idea that all that happens with different arm slots is that the spin axis of the pitch changes. If you’re with me so far let’s continue.

We’re going to return to our extreme overhand righty pitcher in the Okajima mold. Here’s a progression of pitches as seen by the batter from one end of the spectrum to the other. We’re marking 45 degree intervals as we go. I’ve named them with roughly the popular names we recognize them by. A pitching coach might quibble with the exactness of my names, but for our purposes they are close enough.

Overhand right-handed delivery as seen by batter
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It’s worth noting that once you move away from the extremes of fastball and curveball you start to see some misalignment with the spin that is most evident with the middle pitch, the slider. In fact this football-like or bullet-like spin doesn’t contribute anything to the movement of the pitch. It actually decreases the effect of the spin. If a pitcher threw a pitch with perfect bullet spin it would not move at all—no hop, no dive, no slide, nothing. So a slider is actually an inefficient pitch spin-wise, although this inefficiency in no way lessens its effectiveness. I’ll go into this in more detail in a future article, but suffice to say, when you have off-kilter spin the direction of the movement doesn’t change; it just gets reduced somewhat. Also, this off-kilter spin is the source of the dot that some batters with especially keen eyesight sometimes observe on cutters, sliders, and slurves. The dot forms because there’s a dark colored (red in relation to the white ball) seam at the axis of spin and it is tilted into a position where it is visible to the batter.

Now that this little sidebar is out of the way, let’s look at the same progression from a sidearmer.

Sidearm right-handed delivery as seen by batter
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Make sense? But what are those intermediate pitches, the cutter, slider, and slurve doing exactly? It’s easy to get confused so let’s look at a Rosetta stone of sorts that can translate pitch movement into terms we can understand. The names correspond to how pitches move from a conventional “high ¾” arm slot.

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So by matching up the pitch movement with this key we can see that a sidearmer’s fastball moves like a screwball, his cutter moves like a sinker, his slider like a fastball, his slurve like a cutter, and his curveball like a slider. This is why these odd birds of the pitching world can be so successful even without the levels of raw talent other conventional pitchers have. They have a completely different array of pitches than a conventional pitcher, and because they are rare, batters are not familiar with what kinds of pitches they will see. When a batter has to face submariner Brad Ziegler, whose fastball acts like 90 mph screwball from a conventional pitcher, it’s easy to see why they have so much trouble.

Here’s the big chart with four different arm slots and the progression of five pitches we have already been discussing plus the sinker, which is a lot like a cutter except with movement in the opposite direction.
For the purposes of this chart, the slots as described have the following “clock” angles.
1. Overhand: 12:00
2. Three-Quarter: 1:30
3. Sidearm: 3:00
4. Submarine: 4:30

I’ll leave it at that with the one parting comment that I already mentioned at the beginning of this article: the most common arm slot is the “high ¾”. Most pitchers will fall somewhere in between the overhand and ¾ arm slot.
I’d like to thank former major league pitcher and sidearmer Dave Baldwin. He was invaluable in providing some real-world sensibility to the many revisions this article went through.

Overhand right-handed delivery as seen by batter
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Three-quarter right-handed delivery as seen by batter
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Sidearm right-handed delivery as seen by batter
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Submarine right-handed delivery as seen by batter
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