Stats All, Folks: What is spin rate, and why exactly does it matter? -
Paul Folkemer

Stats All, Folks: What is spin rate, and why exactly does it matter?


Back by popular demand (or maybe despite it), it’s Stats All, Folks!

I began this feature last year as a primer into the world of sabermetrics and analytics. My goal is to provide a basic introduction to advanced baseball statistics for people who want to learn more. Last year, I discussed WAR, FIP/BABIP, Launch Angle/Exit Velocity and Defensive Runs Saved, among several others.

Turns out, there are even more stats out there. Who knew? So, I’m back for another round in 2018.

Disclaimer: I don’t consider myself an expert on sabermetrics. I’m not a licensed and bonded sabermetrician with a degree from Stats University. I’m just a guy who finds this stuff interesting. And with sabermetrics and advanced stats being such a crucial part of how most teams operate these days, I think it’s important to take a closer look at these metrics and what they mean.



Let’s turn to today’s topic: spin rate.

What is spin rate?

Spin rate is a measure of how quickly the ball spins after the pitcher releases it from his hand.

Since when has this been a thing?

Well, baseballs have always spun. (Very insightful, I know.) Until very recently, though, we didn’t have a precise measurement of how much they spun. It’s not exactly something you can track with the naked eye. But starting in 2015, MLB’s Statcast has made spin rate data available to the general public. And we’re beginning to understand why spin rate is so important.

Well? Why is spin rate so important?

I’m glad you asked. The simple answer is that spin rate affects where the ball ends up when it reaches the batter. For a fastball, the higher the spin rate, the higher the ball will stay in the zone. The lower the spin rate, the lower the ball will drop.

For a breaking ball, it’s the opposite — the higher the spin rate, the more the ball will drop; the lower the spin rate, the more it stays up.

Why does that happen?

Because of physics. When a baseball is thrown with backspin — as a fastball is — the ball will push downward on the air as it moves, which in turn causes the air to push upward on the ball. (Think back to science class and Isaac Newton’s laws of motion: for every action, there is an equal and opposite reaction.)

So, the more spin on the ball, the more the air pushes it upward, which causes the ball to stay a little bit higher for a little bit longer than when it’s not thrown with as much spin. The ball doesn’t actually rise, of course; it just doesn’t sink as quickly.

A breaking ball, on the other hand, is thrown with topspin. The ball is spinning in the direction of gravity instead of pushing against it. So, the more the ball spins, the faster it sinks.

Yay, science!

So, which is better for a pitcher? High spin or low spin?

Well, that depends. What type of pitch are you throwing, and what results are you hoping to get from the batter?

The first few years of Statcast data have shown that, in general, a fastball thrown with high spin will lead to more swinging strikes and fly balls. That’s because a high-spin fastball will stay a little higher in the zone than the hitter expects, and he’s more likely to hit the bottom of the ball or miss it entirely. By the same token, a low-spin fastball usually leads to more ground balls, because it drops a bit more than the hitter anticipates and he’ll often top it into the ground.

So, pitchers can be successful with either high spin or low spin on their fastballs. The danger zone is in the middle — a spin rate that isn’t particularly high or low. When that happens, the pitch tends to stay straight without much movement, and hitters are better able to make good contact.

For a breaking ball, a higher spin rate leads to more grounders. Remember, high spin rates on breaking balls help the ball sink more. That makes it difficult for hitters to get under it. A low spin rate on a breaking ball is riskier territory; lower spin means the ball won’t break as much, leading to hangers that hitters can crush.

Let’s also consider changeups. Since changeups are thrown with the same motion as a fastball — using backspin — but are meant to be slower, a low spin rate is generally more effective than a high spin rate for these. This gives them a bit more movement down in the zone.

Wasn’t there some sort of controversy about spin rate earlier this year?

Yes. Cleveland Indians pitcher Trevor Bauer, an avid fan of sabermetrics, caused a firestorm when he implied that Houston Astros pitchers were increasing their spin rates through the use of foreign substances on the ball.

“I’m not accusing them of cheating,” Bauer said May 2. “That being said, there is a problem in baseball right now that has to do with sticky substances and spin rates. We might not have had the technology before to measure how sticky stuff affects the ball, how it spins, how it moves. But all that research is clear now. We know how it affects spin rate and we know how spin rate affects outcomes and pitches and movements that have a big difference in a game.

“You have guys using sticky stuff every single time they pitch, increasing their spin rate by 200-300 rpm (revolutions per minute) and having a massive competitive advantage.”

For the record, there is no evidence that the Astros have been using foreign substances, although they do lead the majors in average spin rate (2,374 rpm). It’s also worth mentioning that Bauer himself has increased his average spin rate nearly 250 rpm, from 2,171 to 2,413, since the 2015 season.

You do know this site is called Baltimore Baseball, right? Will you be discussing the Orioles at some point?

Yes, yes, fine. Let’s use some Statcast data for 2018 Orioles pitchers as an example of how spin rate can have an impact on pitchers’ performances. Specifically, we’ll look at the Orioles’ spin rates on fastballs.

The Orioles with the four highest spin rates — Tanner Scott (2,424 rpm), Dylan Bundy (2,411 rpm), Pedro Araujo (2,365 rpm) and Mychal Givens (2,362 rpm) — are all pitchers who have averaged more than a strikeout per inning this season. That falls in step with what we’ve gathered from Statcast data; fastballs thrown with high spin rates induce more swings and misses. Those four pitchers’ ability to spin their fastball is part of what has helped them rack up the strikeouts.

Of course, there’s a lot more to pitching than spin rate. Araujo (7.03 ERA) and Scott (5.56 ERA) are proof that a high spin rate alone doesn’t necessarily make a pitcher successful.

It might not surprise you that the lowest spin rate on fastballs belongs to Richard Bleier (1,883 rpm). As discussed earlier, a low spin rate on a fastball might not help whiff batters, but it can be very effective for forcing weak contact and inducing grounders. That’s what Bleier has done best en route to his superb 1.42 ERA this season.



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