The Astros’ Chris Devenski and Large Velocity Gaps

In the second half of the double-header between the Twins and Astros today, Chris Devenski will take the mound for the Astros. He owns an 80 mph changeup and a 92 mph fastball, give or take some ticks, and that differential is the fourth-biggest one among starting pitchers since 2014. That fact alone should make his changeup a great one when it comes to whiffs.

We’ve known for a while that movement and velocity differential are important to a changeup, but seeing as how the relatively ineffective John Lamb possesses the league’s second-best differential — and because the changeup works, in no small part, because of its relationship with the fastball — it seems fair to wonder, as someone in my chat did today, if a changeup which features too great a velocity differential might also suffer from ineffectiveness. In theory, an 80 mph changeup might look the nothing like a fastball. And if that’s the case, how could it fool the batter?

In practice, though, it looks like the bigger the difference, the better the results, more or less. Here are all changeups thrown 300 times in the last three years, plotted by their velocity differential against their swinging-strike rate. Color denotes the fastball velocity, just to separate out the slow, slower, and slowest pitchers.

The general tilt of the graph is obvious, but bucketing can help us understand this a little better. Among the 35 changeups than feature more than a 10 mph velocity difference off the fastball, only two have produced whiff rates that are lower than average: Wily Peralta (10.7 mph diff, 10.5% whiffs) and Odrisamer Despaigne (15.1 mph, 10.2% whiffs). And even those two aren’t that far from the average changeup, which gets 14% whiffs.

Devenski, just by belonging to the group that features a 10-plus mph difference between fastball and changeup, is likely to have a 18.7% whiff rate. That’s the whiff rate of the group, at least.

Of course, arm speed is meaningful. Anthony DeSclafani had a changeup with an 8 mph velocity differential and good movement on the pitch going into last season. That’s not Devenski-level, but by all account sit should have led to an average changeup. It hasn’t. What DeSclafani admitted to me was that he was dragging his arm and batters could tell what was coming.

So it’s not just differential alone. What “helps” this graph become clearer is that, once a pitcher has a better than 10 mph gap, the pitcher has no excuse not to have good arm speed on his changeup. In other words, a 9 mph gap is still above average, too. The pitcher has leeway to speed up his arm on the change.

Let’s watch Devenski fall off the mound throwing a fastball.

Now here’s the change, on the next pitch.

As a batter facing that combo, you have to time your bat to the 92. If you start your swing for a fastball, it’s hard to hold up when the change comes. That nearly 12 mph gap means that the changeup will show up at the plate around .05 seconds after the fastball would have. By then, your bat will be further through the zone and you will be that much closer to whiffing.

Devenski’s slider (81 mph) and curve (77 mph) are fairly slow for breaking balls, which means it’s an open question if they are plus pitches for him. And that’ll be something to watch tonight. Once you get your fill of those bugs-bunny changeups, of course.