Is Spin Rate the key to a great heater?

We are kicking off our series on how to apply pitching data by talking about 4 Seam Fastballs. Though it may seem like a simple pitch, there’s a lot we can learn about a 4 Seamer by looking at pitching data. One of the earliest observations of the pitching data revolution was that 4 Seamers with more spin seemed to be valuable. But is Spin Rate the key to a great heater? It’s not quite that simple. We’ll be discussing the key metrics to understand the 4 Seam Fastball and even looking at a couple of examples from MLB pitchers.

What’s the goal of a 4 Seam Fastball?

Of course, the simplest goal of a 4 Seamer is to miss bats. But how do we actually do that? Speed is one element. A faster pitch reduces a batter’s time to react. The other element is pretty simple. The batter swings the bat where they think the ball is going. So, we want a pitch that goes somewhere other than where the batter is expecting. With a 4 Seamer specifically, we want the ball to end up higher than the batter’s eyes tell them it will be.

What Metrics are most important when looking at a 4 Seamer?

Vertical Movement

If we want a pitch that ends up higher than the batter expects, the first metric we’re going to look at is Vertical Movement. In this case, we mean induced movement, or the movement created by spin. At the MLB level, an average 4 Seamer has about 15 inches of upward Vertical Movement. As it turns out, Vertical Movement doesn’t change much with Speed, so pitchers at lower levels can create similar amounts of Movement. So if we imagine a Fastball with 19 inches of Vertical Movement, it’s probably going to end up about 4 inches higher than a batter expects. This is mostly true, but it’s not actually quite that simple - more on that later. 

Spin Rate

What about Spin Rate? It turns out that Spin Rate is one element that helps to create Vertical Movement. We prefer to think about Spin Rate in terms of Spin Velocity Ratio (Spin Rate divided by Velocity in MPH). SVR stays consistent across velocity, so the average MLB SVR is pretty much the same as the average high school SVR. An SVR of about 23-24 is pretty average for a 4 Seam Fastball, so if you’re able to create a higher SVR, you have one of the tools to create an unexpected amount of Vertical Movement. (Check out more about here.)

Spin Direction and Spin Efficiency

Two other tools pitchers use are Spin Direction and Spin Efficiency. Spin Direction (the blue arrow on the pitchLogic app) points in the direction of movement, so if you are able to get your Spin Direction closer to 12:00 more of your movement will be Vertical. Spin Efficiency describes the percentage of your spin that contributes to Movement. A higher Spin Efficiency creates more overall Movement, both Vertical and Horizontal. These two exist in a sort of balance. As a pitcher redirects the Spin Direction toward 12:00 (or toward their glove-side), the Spin Efficiency naturally decreases. This is just another way of describing cutting the ball. Finding the sweet spot to maximize Vertical Movement is a little different for each pitcher.

Do the metrics of a "good" fastball differ for pitchers with high and low arm slots?

Let’s look at some real-life examples. Above we have the metrics of two MLB pitchers. On the left we have Justin Verlander. He’s creating 18 inches of Vertical Movement. We can see that he’s throwing from a high Arm Slot (see the yellow arrow above), which is helping him create a high Spin Direction. At 25.8, his SVR is well above the average of 23 - 24. His Spin Efficiency is close to 100%. He’s doing basically everything we look for in a 4 Seamer. No surprise!

On the right we have the Seattle Mariners’ Bryan Woo. He has an average SVR, a lower Spin Efficiency, a fairly average Spin Direction, and a slightly below average Vertical Movement. That doesn’t sound like what we’ve been talking about…

But here’s the surprise… these were both highly effective pitches in the 2023 season. In fact, they performed almost identically. By looking at outcomes alone, Woo’s 4 Seamer was actually slightly better than Verlander’s. So why is that?

Let’s go back to that goal of missing bats. Batter’s don’t perceive every pitch the same way. Woo throws from a much lower Arm Slot than Verlander. Batters naturally expect a Fastball from that slot to run more than carry. Woo’s 14 inches of Vertical Movement are more surprising than Verlander’s 18. So Vertical Movement is still a key to success for both pitchers, but there isn’t one magic number that’s right for every pitcher. It’s all about creating movement that’s surprising to a batter.

What is a “dead zone” fastball?

A “dead zone” fastball is sometimes described as a fastball with an average amount of movement. It’s right in the middle of what a batter expects to see. Like successful fastballs, the “dead zone” is really relative to a pitcher’s Arm Slot. If a pitcher with a 1:15 Arm Slot had Bryan Woo’s movement numbers, that would be a “dead zone” pitch for them. But with Woo’s 2:15 Arm Slot, his “dead zone” might be 8 inches of Vertical and 14 of Horizontal.

How do we work with a pitcher who struggles to throw a good 4 Seam Fastball?

There are a number of natural tendencies that help some pitchers throw good 4 Seamers. A high Arm Slot, a high SVR, and the ability to move Spin Direction significantly above Arm Slot while maintaining a high Spin Efficiency can all be assets for throwing a good 4 Seamer. If a pitcher displays one or more of these, it can just be a matter of fine tuning things to find their best pitch shape. Often pitchers are cutting the ball either too much or too little and an adjustment can help them find the right balance between Spin Direction and Spin Efficiency.

Not every pitcher has to have an exceptional fastball. An average fastball with great command or great secondary pitches can still be a reliable tool. There are plenty of pitchers at the MLB level with average 4 Seamers.

Some pitchers may not display any of these tendencies. We think it’s critical to understand each pitcher’s unique strengths. In these cases, it can often be beneficial to explore a 2 Seam Fastball (also called a Sinker). The same characteristics that can make it hard to throw a great 4 Seamer can help to create a great Sinker. We’ll leave a discussion about Sinkers for another day.

Let us know your thoughts on 4 Seamers.