Using Sabermetrics for Fantasy Baseball: Spin Rate

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. It has also become controversial as of late due to allegations of pitchers using foreign substances to increase their spin.

Unfortunately, the baseball world has done a lousy job conveying what spin rate really means. The result has been a ton of fantasy managers who know that spin rate exists, but very few use it to improve their 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. Let's start with fastballs.

Interpreting a Fastball's Spin Rate

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 complement their whiffs. 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.

For example, Mike Minor's four-seam fastball averaged 2,650 RPM in 2019 to lead all MLB starters. Its 9.4 SwStr% was very good 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 (41.5% FB%) and a high IFFB% (28.9%), suggesting that it produces pop-ups as expected as well. Minor's fastball is clearly a weapon.

However, Minor did not possess the best four-seamer in MLB despite pacing the pack in spin rate. Justin Verlander's average fastball spin rate of 2,574 RPM ranked 15th in MLB (minimum 250 total pitches thrown), but bested Minor's in all of the metrics cited above: 14.3 SwStr%, 55.6 FB%, 25.5 IFFB%. The reason why is that Verlander's fastball gets more movement out of its spin than Minor's.

We have to consider "gyro spin," 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 gyro spin and it has no impact on where the bullet ends up. A metric called "Active Spin" measures how much spin is actually affecting a ball's trajectory. Verlander paced baseball with an Active Spin rate of 98.5% on his fastball in 2019, while Minor's 67.8% Active Spin rate was much less impressive.

2020 was a lost season for both pitchers above. Verlander missed nearly the entire campaign and figures to be out for 2021 as well. Minor pitched to a ghastly 5.56 ERA over his 56 2/3 IP last season, but his elite spin rate remained about the same. With more Active Spin, he could be a breakout candidate in 2021 despite his advanced age.

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 compared to their high-spin counterparts. However, this can be a dangerous way to live. Contact managers need a lot of things outside of their control to go right to become fantasy assets, so fantasy managers should look for high-spin strikeout artists whenever possible.

Evaluating Spin Rate on Secondary Offerings

Unlike fastballs, changeups usually want a low spin rate to maximize how much they move. For instance, a changeup was Anibal Sanchez's out pitch in 2019. It posted an 18.7 SwStr% and 51.4% chase rate, suggesting that opposing batters had no idea where it was going to end up. The reason why is its spin rate: it averaged 1,447 RPM that year.

Sanchez's changeup averaged an even lower RPM of 1,261 RPM last season, and its strikeout numbers were even better at 19.1 SwStr% and 43.6% chase. Unfortunately, Sanchez used it as his primary pitch instead of setting it up with a 4-seamer and cutter the way he did in 2019, leading to a 6.62 ERA over 53 IP. The example goes to show you the importance of having more than one solid pitch in your repertoire.

Breaking pitches usually want high spin rates. Unlike fastballs, breaking offerings have topspin, or spin toward the ground, which can help guide the ball down if contact is made. Breaking pitches tend to be a given pitcher's strikeout pitch though, so managers 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.

There are enough variables in play here 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 (such as Verlander's four-seamer) or if it was probably a fluke.

Conclusion

To summarize, spin rate is measured in RPM. Fastballs can be good with high or low spin rates, but higher spin rates tend to translate better to fantasy. 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, gyro spin can distort spin rate readings, meaning that you should always combine spin rate with other metrics in your analysis. Check out these articles to learn how to apply other advanced metrics to your fantasy prep.

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