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Spin rate has become one of the most recognizable Statcast metrics, with supporters of a given pitcher highlighting his spin rates to make their case.

Unfortunately, the baseball world has done a lousy job conveying what spin rate really means. The result has been a ton of owners who know that spin rate exists, but very few who can use it to improve their fantasy rosters.

This article will teach you everything you need to know to fold spin rate into your pitcher evaluations. We'll also illustrate the efficacy of spin rate using Pitch Info data from actual pitchers. Let's get started!

 

How to Interpret Spin Rate

Spin rate is measured in RPMs, or Rotations Per Minute. Each pitch type has its own baseline numbers, so a high-spin fastball might have an average spin rate for a curve. Comparing different types of pitches by spin rate is rather pointless, so try to focus on how any given pitcher's offering compares to the same pitch type thrown by other arms.

So, are higher or lower spin rates better? The answer is that it depends on the type of pitch you're looking at and what you want from the arm in question. Let's start with fastballs.

The average spin rate for fastballs ranges from 2,100 RPM to 2,400 RPM. Heaters with spin rates above this range tend to have "late life" and induce more whiffs than your average heater. They usually have backspin, or spin against gravity, that guides the ball weakly into the air if contact is made. This allows them to post elevated pop-up rates to compliment their whiffs.

For example, Yu Darvish's 4-seam fastball averaged 2,500 RPM in 2017. Its 10.7% SwStr% was elite for a heater, so he got the whiffs we would expect from a high spin rate. It also had a distinct fly ball tendency when put into play (40.3% FB%) and a very high IFFB% (26.6%), suggesting that it produces pop-ups as expected as well.

It's worth noting that fastball spin rate is positively correlated with velocity, meaning that a pitcher with a velocity spike may also experience a spin rate jump. Mike Minor was a good example of this last year.

If you're looking for a contact manager instead of a strikeout artist, you want a spin rate below the average range above. Low-spin fastballs produce weakly-hit ground balls and a lower slugging percentage against than their high-spin counterparts.

There are fewer examples of this type of arm, but Mike Montgomery's 2017 season provides a good illustration. His 4-seamer averaged 1,841 RPM last year, producing a GB% of 59.8%. Montgomery's ERA (3.38) was significantly better than his xFIP (4.35), but his low spin rate suggests that he can continue to beat his traditional indicators and be a nice volume arm in fantasy.

Therefore, high and low spin rates are both good for fastballs. You want to avoid pitchers with average fastball spin rates, as they lend themselves to neither strikeouts nor weak ground balls. For example, we saw Robbie Ray get considerably better last year by abandoning his sinker. It averaged 2,268 RPM in 2016, preventing it from contributing Ks (6.7% SwStr%) or weak contact (46.5% GB%, but .422 BABIP). Hitters have slaughtered the pitch for a .332/.389/.494 line over Ray's career, so 2016 was not a fluke. Pitches like this don't help fantasy owners at all.

Unlike fastballs, changeups usually want a low spin rate to maximize how much they move. For instance, a change is Chris Devenski's signature pitch. Last season, it posted a 24.5% SwStr%, 40.3% Zone%, and 46.3% chase rate--all excellent numbers.

The reason why is spin rate. It averaged 1,514 RPM last year, 492nd in MLB among changeups. To put that number into perspective, R.A. Dickey's knuckleball--a pitch defined by its lack of spin--averaged 1,533 RPM last year. This low spin rate helps Devenski's change move so much that batters can't follow it, often making them look foolish at the plate.

Breaking pitches usually want high spin rates. Unlike fastballs, breaking offerings have topspin, or spin toward the ground, that can help guide the ball downward if contact is made. Breaking pitches tend to be a given pitcher's strikeout pitch though, so owners generally aren't looking for any kind of contact on them. Breaking ball spin rates are therefore the least important to look at, but may provide interesting information at times.

Finally, we have to consider "gyrospin," alternatively called "useless spin." If you've ever seen a bullet in slow-motion, it rotates slightly while flying straight to its target. That rotation is gyrospin, and it has no impact on where the bullet or the baseball ends up. Sadly, there is currently no way to separate this useless spin from useful backspin or topspin, meaning that spin rate can lie to you.

This means that spin rate should never be considered on its own. Instead, start with Pitch Info and then use spin rate to confirm if a given pitch can sustain its elite performance (Darvish's 4-seamer, Devenski's change) or if it was probably a fluke.

 

Conclusion

To sum up, spin rate is measured in RPM. Fastballs are good with high or low spin rates, but the area in between offers no benefit. Changeups want as little spin as possible to maximize their movement. Breaking pitches typically benefit from higher spin rates, but it's not as clear-cut as it is for fastballs and changeups. Finally, useless spin can distort spin rate readings, meaning that you should always combine spin rate with other metrics in your analysis.

Next time, we'll take a look at what Statcast metrics such as Barrels and average exit velocity mean for pitchers.

 

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