Should Zack Godley Throw the Changeup More?

Things are going well for Arizona starter Zack Godley. He’s among the top 25 of all pitchers this year no matter how you measure value, his team comfortably occupies the first Wild Card spot, and he’s outperforming expectations. Some of those expectations might have been muted because, at first glance, he looks like a run-of-the-mill sinker/breaking-ball pitcher without a sufficiently good changeup to battle lefties. But then you look at the results on his change and you’re tempted to tinker, to suggest he should throw it more. Dig a little deeper, though, and things aren’t as clear.

Take a look at how Godley’s different pitches have performed when it comes to key results. Let’s highlight the best ratios.

You can see why Godley’s had such success: he can use his fastballs for grounders, his cutter and curve for whiffs. He throws that combination of pitches roughly 90% of the time.

Everything falls in line with his overall results until you settle down on the red boxes. Man. This is a sweet changeup! Why doesn’t he throw it more often if it gets top-shelf grounders and whiffs?

The answer lies deeper — in this case, with the movement on his changeup. Here are Godley’s pitches ranked by the relevant movement, spin, and velo aspects for each type. In each case, a high percentile is good.

Here, you’ll notice that the curve, sinker, and cutter all share a similar pattern. Godley uses good velocity on the breaking stuff, paired with great drop on the sinker, to pair grounders with whiffs.

And the changeup once again looks okay here. It’s not great horizontally, sure, but couldn’t it work as a straight changeup with top 25% drop and velocity gap?

Yes. Except for one thing: I cheated.

For these calculations, I found the movement and velocity gap on Godley’s changeup relative to his four-seamer. Thing is, Godley’s only thrown 20 four-seamers all year. If you look for the movement and velo of Godley’s changeup relative to his sinker, though, the results are much less impressive. All of a sudden, he’s in the 24th percentile for drop and in the 54th percentile for velocity gap, along with some of the worst horizontal movement in the game.

Of course, he could pair it with the four-seamer. But he hasn’t shown much inclination to do so. Of the 20 four-seamers he’s thrown this year, only once has he followed it with a changeup. Maybe it’s the spin that doesn’t line up, or maybe Godley just doesn’t want to throw his vastly inferior four-seamer much, since it’s poor in every aspect that normally makes a four-seamer good.

So it’s true that Godley’s changeup is getting good results in a small sample. But it’s also true that we should define the excellence of a particular pitch in the context of a repertoire and not simply the whiffs or grounders it’s generated on its own.

It’s funny, too, because if you look at this changeup by itself, it does look like a good one.

But then look at the sinker that the hitters have been timing all day.

Then, especially when the sinker is more 91 than 94, the changeup becomes what the numbers say it is: a straight, below-average changeup. That doesn’t mean it can’t work wonders for Godley in its current context. That context seems to be when he’s ahead in the count or has two strikes against a lefty, the only time when his usage of the pitch drifts much north of 7-10%.

It’s probably okay, anyway. With a sinker, cutter, and curve, Godley has what he needs to combat lefties. Curves traditionally have reverse platoon splits, even tight curves like the one Godley uses. He doesn’t have a huge observed platoon split (3.41 FIP vs. LHB, 3.10 vs. RHB), and his arsenal doesn’t suggest a weakness there.

Godley’s changeup has worked well this year, and is important part of that three-and-a-half-pitch arsenal. He still probably shouldn’t throw it more often.