Nate Karns and Useful Spin

When the Rays acquired Nate Karns from the Nationals back in 2014, the story was that he had fastball velocity and a power curve, and we’ll see about the changeup. We saw the changeup, and it was good enough, and the curve was as advertised. Unfortunately, something happened to the fastball along the way.

The Rays sent Jose Lobaton and Felipe Rivero to the Nationals for that curveball and hoped on the change. The change looked good in 147 innings for the Rays in 2015, so the Mariners took a leap that offseason, sending Brad Miller, Logan Morrison and Danny Farquhar to the Rays for Karns, right-hander C.J. Riefenhauser, and center fielder Boog Powell. Now, after a poor year, Karns has been traded again — to the Royals, this time — for outfielder Jarrod Dyson.

What happened last year, when Karns had an ERA over five? The curve and the change were fine in Seattle! But in the meantime, something may have happened to Karns’ fastball. And it could have to do with useful spin. Kansas City has to hope that what broke is fixable.

Between 2015 and 2016, the changeup and curve were largely the same for the right-hander. Karns had the same spin and drop on his curve, and it even got a little bit harder — and those are the three most important variables that I’ve identified for the curve. Both years, it got 13-14% whiffs. Both years, Karns had the same velocity gap and movement numbers on the changeup. Both years, it got above-average whiffs.

Karns’ changeup isn’t as good as the curve — it has below-average velocity gap and the movement numbers are middling — but both pitches look to be decent, and relatively consistent, over the last two years.

Well, in process, maybe. Not in results. The change this past year allowed a slugging percentage that was 100 points higher in 2016 than it was in 2015. But it wasn’t the changeup’s fault. It was the fastball’s fault. You define the changeup off the fastball, and the fastball has been different. Take a look at raw and then fastball-defined movement on the changeup over the last two years.

Because the fastball changed, the changeup — which looks like it remained the same — was worse by comparison. That’s still good fade relative to his straight fastball (4.4 inches vs. the average 2.5 inches of difference), but his changeup went from secretly having nearly an inch more drop than average to being exactly average when it came to drop.

Add up the different aspects on the changeup, and it’s not great now. Once the most improved changeup of the first half of 2015, the pitch now has bad velocity gap, average drop, and above-average fade. As a change of pace, it’s still getting whiffs, but the fact that it allowed a .188 isolated slugging percentage last year may have been no accident. But don’t blame the change; it’s still acting the way it has always acted.

What’s going on with that fastball? Why did it lose rise? Spin might be the reason here, in terms of lost spin and lost useful spin.

Here are two related traits of Karns’ fastball from the last years:

In 2015, Karns’ fastball featured among the best rise and spin in the majors; in 2016, he finished in the bottom half among qualifiers. Given that Trevor Bauer could find no way to improve his fastball spin on purpose, this could be seen as unmitigated bad news — Karns lost spin, and that lost spin devastated his once-elite “ride” on the fastball. Batters used to see the ball an inch higher at the plate than they expected, and now the fastball is worse than average in that respect.

Rarely do you see this combination of words, but they are: the pitcher’s injury history provides some hope here. In two different ways, actually. Driveline Baseball has said that they’ve found some evidence that a drop in spin rate was a marker for unhealthy fatigue. Take a look at Karns’ rolling spin rates over the course of the season last year, and you see a decline into two exits (July 30 and September 1) for a lower back strain.

It doesn’t explain everything, because in 2015, Karns averaged in the mid-2300s with his spin, and our “healthy” 2016 Karns didn’t live there long. But it does provide hope that Karns can regain some spin with better health.

Take a look at another, related graph. This one shows the average release point height for Karns’ fastball over time.

This doesn’t look hopeful, but it is. Why? Because, if his health is any better, it’s fixable. It’s a mechanical thing. He has to get on top of the ball better. A higher release point would help the ball ride more — with or without a return to better spin days.

It has to do with useful spin. Not all of the spin on a thrown baseball contributes to the movement of the ball, as professor Alan Nathan has shown. Some spin is “gyrospin” or spin perpendicular to the path of the ball. By dropping down, Karns is, by definition, imparting more sidespin on the ball, because his release point is less over the top. That means less useful spin with respect to ride.

Maybe it’s all too much negativity about Karns’ fastball for you. The fact that both his total spin and useful spin are down is obviously not a great thing. And back strains can be tricky. Maybe the 29-year-old won’t recover his old No. 1.

But the fact that there’s a link here to that specific injury could also be hopeful! If time off allows him to recover, he now has two different ways to recover the fastball. He can work on his release point and standing tall, in order to more effectively harvest the spin he’s got, or perhaps a healthy Karns will throw a higher-spin fastball.

If that sounds like too much hope, let’s return to the fact that Karns, despite his troubles, has nevertheless produced a top-30 strikeout rate among starters over the last two years (minimum 200 innings thrown). That’s a good place to start.