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Spin efficiency: definitions, implications, and everything else you need to know

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The concept of spin rate isn’t worth much without understanding spin axis and maximizing spin efficiency

Washington Nationals v Cincinnati Reds Photo by Dylan Buell/Getty Images

Concepts such as spin rate have been around the game of baseball for a few years now, as we all try to understand what’s behind the beautiful art of pitching. Spin rate is nothing more than the number of times, or rate, the ball spins after leaving the hurler’s hand. Revolutions per minute (RPM) is the unit we use to measure it.

We tend to think that spin rate is directly correlated to ball movement and that every pitcher with a high spin rate will miss more bats. That is not always the case, though.

Just as high velocity doesn’t always result in more swings and misses when it comes to fastballs, a high spin rate doesn’t always correlate to missing bats either. Sure, it helps, but it’s not the be-all, end-all of getting whiffs.

That’s where the concept of spin efficiency comes in. It is the percentage of spin rate that contributes to pitch movement. In this case, the closer the spin efficiency (or active spin, as it’s also called) is to 100%, the better (in most cases, because a lower efficiency is tied to more movement in the specific case of changeups).

For fastballs, though, a high spin efficiency is the key to unlocking its full potential. For heaters, the movement profile (how much the pitch moves vertically and horizontally) and how the movement is created are perhaps more important than velocity or raw spin rate.

How do pitchers maximize spin efficiency? We welcome another useful term: spin axis. There are three things that impact spin axis: arm slot (heavily), wrist angle, and the orientation of the fingers at the moment of throwing the pitch.

Spin axis directly impacts the direction in which the ball will move. To measure it, we need to picture a clock: as Trevor Powers of Prospects 365 explains, a pitch with perfect backspin will be on a 12:00 axis. A ¾ arm slot pitcher and a side-armer will get very different spin axes.

In a way, spin efficiency tells us how legit the pitcher’s spin rate is. A 100% spin efficiency, or a high-efficiency fastball for that matter, is important because it creates the famous “rising” effect on fastballs, which is essentially preventing them from sinking and catching too much of the heart of the plate.

Heaters with high efficiency, close or at 100%, have what is commonly called as “life,” because they will keep their trajectory instead of fading into the middle of the zone, where they are much more vulnerable.

Here is a perfect example of how spin efficiency affects fastball movement:

Having explained all this, we will look at the pitching leaders in active spin during the 2021 season:

There are some solid major leaguers in there. Tyler Mahle, Ian Anderson, Devin Williams, Austin Gomber, Lucas Giolito, Zach Plesac, Drew Smyly, and Jake Odorizzi either had a good 2021 or have enjoyed recent success.

For the sake of fun, let’s see those who finished on the other end of the spectrum:

There are also solid pitchers in there, too, even the NL Cy Young award winner Corbin Burnes.

Burnes, as you probably know, makes his living while making his fastball to cut rather than rise. Other top pitchers in this list, such as Marcus Stroman, Spencer Turnbull, Andrew Kittredge, Joe Musgrove or Framber Valdez don’t go with the “throw your four-seamer up in the zone” manual, and they do just fine.

As with everything in life, there is not just one way to find success, so spin efficiency is not the only path to stardom. But it’s a very useful concept, one that works for most pitchers who have learned the craft of maximizing the spin rate of their fastballs.

Andrés Chávez loves the game of baseball and writes about it at Beyond the Box Score, Pinstripe Alley, and other sites. He is on Twitter as @andres_chavez13