Revisiting The D’Backs Young Rotation

This spring, the Arizona rotation was a fascinating mix of imported and home-grown youth, and Josh Collmenter and Jeremy Hellickson. Each of the youngsters gave us a point of emphasis this spring, and now that they’ve each had a few chances to show their work, we could give out some first semester grades. And maybe figure out how who’s at the head of the class.

Chase Anderson might have the best argument for valedictorian. He’s had the best ERA and peripherals, and that’s not too surprising, since he was the guy that had the most experience. And if Rubby de la Rosa has a plus changeup, you could say that Anderson has two.

So Anderson spent the spring working on his two-seamer, he said. If you look at PITCHf/x and his homer and grounder rates, you’d think he has succeeded in that effort. By that measure, he’s upped his usage of the sinker from 18% to 27%. His ground-ball rate has gone up from 40% to 43%. It’s a tempting narrative, especially since it fits into what the pitcher himself said earlier this year.

But head on over to Brooks Baseball, and they have him throwing almost exactly the same amount of two-seamers (21% last year, 20% this year). Maybe he improved the actual pitch — it has maybe a third of an inch more fade this year — but maybe he didn’t (it has a half inch less sink).

Anderson hasn’t given up a homer on the two-seamer this year, though, and he’s thrown 135 of them according to Brooks. It’s possible that he’s throwing them lower in the zone — his average height has gone down on the pitch and pitch location has everything to do with ground-ball rate — but it’s also possible that a change in strategy on the two-seamer has really effected his changeup.

Last year, Anderson gave up homers on over 1% of the changeups he threw to lefties, and this year, he’s thrown 148 changeups to lefties without a homer. Last year, Anderson didn’t throw the two-seamer inside to lefties (on the left). This year, he has (on the right). Could it be that sneaking two-seamers across the inside corner of the plate against lefties has kept them from hanging over the plate for the changeup?

Rubby de la Rosa’s homework assignment was to improve his breaking ball. After all, he had this changeup grip that Pedro Martinez taught him, and that’s about the best teacher a guy could have. He’s still throwing a ton of them (only seven starters have thrown more changeups), and his 15% whiff rate on the pitch rates as above average.

But the slider was a work in progress. Not as much any more. Among the 122 pitchers that have thrown the slider 75 times this year, De La Rosa’s 20.4% whiff rate on the pitch ranks 29th — one slot ahead of super rookie with the super slider, Carlos Rodon.

Part of how he did this is mechanical, maybe, as he explained in the spring. And some of it is explained well by this table I’ve stolen from Alex Chamberlain’s post on Rubby De La Rosa’s slider, which is worth a read for his in-depth look. Here are some relevant stats just for his slider:

Year	Usage	O-Swing%	O-Contact%	Zone%	Z-Contact%	SwStr%	xMOV	zMOV	MOV
2014	11.1%	29.4%	56.3%	51.6%	89.2%	9.3%	3.1	1.0	4.2
2015	13.2%	47.5%	47.4%	59.2%	67.7%	20.4%	1.4	1.1	2.4

The pitch got straighter, but it’s working better. For my money, it’s the velocity. His slider is now two ticks faster on the gun, and velocity is generally a good thing for breaking balls if whiffs are on the line. (Really, for any pitch save perhaps the changeup.) Here’s his ‘most average’ 2014 slider on the left, and his ‘most average’ 2015 slider on the right. As much as Chamberlain makes a good point about consistency, the one on the right looks tighter and/or sharper.

If you use the zone percentage on the pitch, it looks like he’s also improved his command on the pitch, which is worth noting. In our research into pitch type peripherals, we found that zone% might actually add information — there’s only limited usefulness to a great pitch, however unique, that you can’t throw in the zone. That might partially explain how Allen Webster ended up in the minors despite bendy pitches that got whiffs (the other part might be the shoulder fatigue he’s currently experiencing.)

Of the three young Baby Backs, Archie Bradley might have gotten the most buzz. But if there was a report card for spring declarations, he’s got the failing grade. He was supposed to work on his changeup, and he’s only thrown seven so far this year. They look a little like this one on average.

It looks like it could be useful in a show-me way. It’s close enough to average at least, even with a half inch less fade than average and a half-inch less drop, because of the league average separation between his change and fastball velocities (8.5 mph). Okay, so let’s give him an incomplete. At least he made an interesting parallel between the pronation in the wrist when throwing a football and a changeup.

The Diamondbacks brought a gaggle of young pitchers into camp this year. Chase Anderson, Rubby de a Rosa, Archie Bradley, Allen Webster, Yoan Lopez, Robbie Ray, and Randall Delgado. Each had something to work on, and each still does. But by first making progress on their checklists, these three have made enough progress on their homework that we should take notice.