It’s exciting to have so many statistics available to us when we’re trying to evaluate our favorite players. From the players’ perspective, though, it’s probably more exciting when those statistics allow them to improve themselves. From that point of view, metrics like launch angle and spin rate probably have a certain appeal that some others don’t: they provide a measurement of something that might help a player understand his game and get better.

There’s one problem, though — with spin rate, at least. Indications are that it’s difficult for a pitcher to change his in any material way. Still, as Jeremy Jeffress may have found, it can provide a window into betterment.

The year-to-year stickiness of spin rate is insane. The r-squared between this year’s spin rate and next year’s is .816, meaning one explains over 80% of the variance in the other. That’s stickier than any results-based statistic, and only slightly less sticky than velocity from one year to the next (.863 r-squared).

That doesn’t stop pitchers from trying to put on velocity from year to year, of course. But there’s a certain point in a pitcher’s career at which “add velocity” isn’t really considered the best way forward. Not the way that’ll work for most pitchers. After all, only 14 pitchers over the age of 25 who pitched 100 innings in both 2015 and 2016 put on a tick of gas or more. Out of 79 chances. Rough odds, at least.

Improving spin rate, especially without improving velocity, is just as tough for a pitcher. But a pitcher can change his approach to better use his spin rate.

We’ve seen a high-spin-rate pitcher do this before. Rich Hill was a sidearmer for a while, but his high-spin curve and fastball combo make more sense from a different slot. Now that he’s “mirroring” that spin from a higher slot, he’s making it hard for batters to discern his curve from his fastball, and he’s getting more ride on his fastball.

Enter Jeremy Jeffress. With a 95 mph fastball, he’s been interesting forever. But if you remember back when he was 26 going on 27, he’d had 10 good innings and a lot of struggle in his career. Maybe spin rate has something to do with this. Maybe that’s not the precise term he would have used, but the idea was similar.

Last year, Jeffress discussed his development as a pitcher with FOX Sports Wisconsin. Of particular interest is the a-ha moment he experienced with Rick Langford at extended spring training for the Blue Jays. Langford told him to try the two-seam grip and to drop his arm down some.

Jeffress has good velocity, but his velocity-indexed spin rate on the four-seam is 4% worse than average. That might have something to do with some of his lesser strikeout rates in the minors — and some of his struggles in the major leagues, too.

His velocity-indexed spin rate on the two-seamer is also below average, by about 5%. However, low spin can benefit the two-seamer, as it leads to more drop. So if you don’t have exceptional spin on the four-seamer, but you do have good velocity, what’s the answer? Dropping down, throwing the two-seamer, and making your lack of spin work for you.

Jeffress went from throwing a straight four-seamer with less than a half-inch of ride to throwing a two-seamer with an inch-and-a-half more drop and fade than your average two-seamer. That’s how he got a 69% ground-ball rate on the pitch last year, and it’s part of why he’s been excellent for three years running. This two-seamer is not flat and boring.

So why write about this now? Jeffress recorded the second-biggest change in arm slot last year, second only to James Paxton in size. Paxton dropped down 5.3 inches and Jeffress 4.5 inches, both significant numbers. You see that hump in the graph above.

This was Jeffress’ second dance with a drastic arm slot change, and it shows how difficult change can be. Maybe you can’t change your spin rate, and so you change your slot to better fit your innate spin. You’ll still have to work. Your body will still want to return to its old ways. Change is never easy.