Pretty often here on the internet we talk about non-elite pitchers as being more or less crap shoots. It’s true, pitchers tend to be more volatile than hitters, mostly because they get hurt more often. Luck can swing an ERA pretty wildly and trying to make bets on run-of-the-mill pitchers is just hard to do in confidence. What will Chase Anderson be like next year? Hell, I have no real idea. I can see a pretty good pitcher and I can see a guy who just doesn’t even make the rotation aside to fill in for an injury in June. That’s not really the position you want to be in with your hurlers and I think we’ve all seen enough of that in Arizona over the last couple of years.

One way that pitchers are like hitters is that they have feelings. Another way that pitchers are like hitters is that they are served well when they have a particular carrying tool. And I’ll be very liberal with “tool” here. Generally when we throw that term out it’s in regard to something mechanical – fastball velocity, command, the ability to hit for power, a strong throwing arm, etc. It’s pretty generally accepted that a hitter needs to have at least one very good to excellent tool to remain employed in the majors. Similarly, a pitcher needs to have one special ability to remain on the mound for any notable length of time. It can be an obscene number of grounders, extreme numbers of fly balls, massive strikeout totals, a minuscule walk rate, whatever. You have to have at least something going for you on the mound.

The above alludes to something you’ve probably read here at Inside the ‘Zona or heard Ryan and I discuss on The Pool Shot. Being in the middle as a pitcher just isn’t a good place to be, at least not from a consistency standpoint. Fly balls at Chase Field are problematic, but when a pitcher is able to rack up an excessive number of fly balls, he moves into a realm of effectiveness, even in a hitter’s park. Being a contact manager is tough, but it can be done effectively. Look no further than Brad Ziegler and soon-to-be-very-rich Darren O’Day. They have wildly different profiles: Ziegler leads the league in GB%, O’Day ranks near the top of the league in FB%. Neither is a flame thrower (although O’Day clearly has the edge on Ziegler) but they’re both effective by generating a certain kind of contact. This principle applies to starters, too, and that’s where we’ll direct our focus today.

Over at FanGraphs, Tony Blengino has been doing some very intriguing work with the batted-ball data that’s available thanks to StatCast. With his help, we’ve been able to see just how well certain pitcher tools (or traits) carry over from year to year. You can read more about that here, and I highly recommend it. For the sake of brevity, let’s just review which traits are stable, less stable and unstable from year-to-year (with correlations in parenthesis – the closer to 1 the more stable, the closer to 0 the less stable):


  • K% (.81)
  • BB% (.66)
  • FB% (.76)
  • GB% (.86)
  • FIP (.65)
  • SIERA* (.72)

Less Stable

  • Pop Up% (.53)
  • ERA (.45)


  • LD% (.14)

Hey look, that’s neat. There are definitely some tools and/or traits that we can feel pretty comfortable about. GB%, K%, FB% and others remain pretty consistent year in and year out, meaning we wouldn’t expect any big swings from one year to the next in those categories. Pop ups/infield fly balls are pretty stable, although not as stable as the others above. We know ERA has it’s issues and that’s why we use FIP and other ERA-estimators here the vast majority of the time. Line drive rate always has been and always will be wildly unpredictable.

*One note: Blengino uses his own personal metric called “tru” ERA, which incorporates batted ball data. This is what SIERA is designed to do, too, and although the two are surely different, I’ve inserted SIERA here to replace “tru” ERA since they’re similar and we know SIERA is the most stable ERA-estimator from year-to-year.

So with this knowledge going forward, we can put a handful of Diamondbacks starters under the microscope to see to what degree we think they may have similar or dissimilar seasons in 2016. Well, actually less than a handful since Jeremy Hellickson got traded recently. We’ll keep Rubby De La Rosa in here for now even though I’m convinced he’s a reliever. With 80 innings pitched as the cutoff, we’re left with Anderson, De La Rosa, Patrick Corbin and Robbie Ray. Here are their 2015 numbers, along with their percentile rank for each category out of 147 total pitchers.

Pitcher Scores

 *click to enlarge

So let’s apply the previous discussion to these four pitchers. Only Rubby De La Rosa was a standout in the ground ball category, and we’d expect him to still get grounders going forward. Because of the volatility associated with line drives, we can more or less assess that Ray, Corbin and Anderson were unlucky and De La Rosa was lucky. For fly balls, Corbin didn’t give up very many, but the sample size of his innings give a little a pause. Ray and Corbin were both good for strikeouts; Anderson and De La Rosa were not. Corbin didn’t walk anyone (again, SSS warning) while Ray issued too many free passes, as did De La Rosa. If we synthesize this, we’d expect these four traits (GB%, FB%, K% and BB%) to translate pretty well to next year, which bodes well for some and not so well for others.

I left ERA and SIERA out of the previous discussion for a reason. These are the “end results” of a lot of the things above. ERA says what happened with all of those grounders, flies, strikeouts, walks and more. SIERA says what should have happened with all of those things. We can look at the ERA numbers and acknowledge that Ray and Corbin had nice seasons (when they were pitching) while Anderson and De La Rosa weren’t very good at all. But SIERA is both more accurate as an indicator of true talent and is more consistent from year-to-year than ERA. By that measure, Corbin really was very good, Ray was just okay and both Anderson and De La Rosa  were still nothing to write home about. We should feel relatively confident that those brief descriptors will carry forward. Lastly, to clarify, I didn’t include FIP because it fits between ERA and SIERA and really why make this any  more complicated than it needs to be?

Here’s what I take from this for each pitcher, for better or worse:

  • Robbie Ray outperformed his peripherals a bit in 2015 and, unless he can get a breaking ball figured out and limit the walks, he won’t get any better than he is right now, which is truly more okay than good.
  • Patrick Corbin was solid across the board, and even though his small sample distorts his numbers a little, his ability to strike guys out and not walk them makes him a potentially top 15 pitcher in baseball.
  • Chase Anderson’s batted ball profile puts him in the danger zone and the drop in strikeouts really hurt him. He’s a rotation filler and nothing more at this point.
  • Rubby De La Rosa got some ground balls and did nothing else well. The fact that he was in the 9th percentile for LD% and still had an ERA and SIERA that were poor says it all. If he can’t get out lefties (never has, probably never will), he’s a RP.

This is the snapshot we’re left with. It holds true at this place and time. That doesn’t mean it won’t change going forward, but armed with some new information, we know that we should expect certain things to hold steadier than others. The ground ball guys will be the ground ball guys, for example. The strikeouts will remain for Corbin, the walks for Ray. We might expect a decrease in line drives for Anderson, Ray and Corbin, and an uptick for De La Rosa.

There are, of course, pieces of this puzzle we cannot predict. Will Robbie Ray finally learn a functional breaking pitch? Will Rubby De La Rosa be moved to the bullpen or traded? Will Chase Anderson be traded or even make the Opening Day rotation? Can Patrick Corbin stay healthy? We can’t know these things for sure. But based on what the pitcher can control and has done in the past, we have a clearer picture moving forward. That picture supports the team’s need to address the rotation in the immediate future, trim the fat (or at least limit it) and not rely too heavily on Robbie Ray’s initial success. If they apply the right context, there’s no reason not to make the necessary changes.

9 Responses to Predicting Diamondbacks Starting Pitcher Success

  1. anon says:

    we all know, robbie was pretty dominate, and didn’t fall apart after a non run support July. His main problem of course too many pitches, not being able to put guys away without a second put away pitch. Rubbie’s splits against lhb k rate against of 15 percent 567 slg which means the 331 babip is slightly lucky its not higher. Man he’s an ace against rhp. And I’m not saying anything but PC wasn’t exactly getting rh’ers out His K rate was good enough though.

  2. Jeff says:

    Very interesting read! I love the advanced pitching statistics and analysis! The only thing that I disagree with, and strongly, is the glass half empty view on DE LA Rosa. I’ve said it before but your personal bias shows through very strongly in your writing. In my opinion, of the problems associated with each pitcher above, the LHB struggle RDR faces is most likely the easiest to adress, much easier than teaching a breaking ball. It could be even as simple as a new plan of attack against lefties which could come with a new pitching coach. He is obviously a very talented pitcher if he is in the 9th percentile of 1 of the most saught after categories in pitching (gb%) PLUS he held righties to an insane 2.5 ERA. One change in plan of attack, preparation, or defensive switch could cut his 6.5 lefty ERA in half and while still a little high, when combined with how he dominates righties, making him a high end 3 or even 2 starter.

    • Jeff Wiser says:

      Thanks for the feedback! I don’t think I’m exactly trying to hide my view of De La Rosa – I’ve been pretty explicit about it because I really do believe, and the number support, that he should not be part of the rotation next season. I do think you may be on to something with his approach, and maybe that’s a sequencing issue – one no one has really gotten a handle on that and how to evaluate it (at least publicly). If he’s not able to get out LHB’s, which there’s no reason to support that he can right now, he really could be a very good RP when facing mostly righties. As you mentioned, he’ll get lots of grounders and some K’s. In the right role, he’s still a useful player.

      • Ben says:

        I think both of your opinions may have some truth to them. There is definitely a chance that Rubby could learn to pitch to LHB better, but it would have to be in a fairly small window of spring training since 2016 isn’t the year for experiments.

        Rubby right now is not worth a rotation slot. Ray right now is worth a slot in the mid / back of the rotation. That is the difference between the two. Additionally, Rubby has much more potential as a reliever than Ray would.

  3. Jeff says:

    I agree with both of you, and I do realize that he could be a superb reliever facing mainly righties. I am not denying that. However starters are far more valuable than relievers are, and I believe that if there is still any potential that Rubby could be a TOR arm you have to exercise that possibility. And Ben I realize that 16 is not the year for experiments and that is why he should be on a short leash, however I think that the offseason is the perfect time for RDLR and the staff to maybe further investigate why he failed so miserably vs lefties cuz frankly it doesn’t make sense to me with his stuff how anyone could knock him around. only thing I can think of is that lefties take advantage of all of RDLRs arm side run and his ball is staying in the zone longer against lefties and maybe if he could move the ball the other way (cutter) or even straighten it out vs lefties he could have more success.

  4. […] Jeff explored earlier this week, of the most commonly used pitching statistics, K% and GB% are the two most stable. They rarely occur together. Britton excels at both. Britton is weirdly good, and weirdly good in a […]

  5. I still have some hope, that Ray is going to be able to get enough work in during the off-season to tighten up that slider of his. If he can, he’s a solid #3 guy in the rotation. If he can’t, he’s still not a bad #5.

    Unfortunately, the team has made it fairly clear that they intend to run with RDLR again in 2016. I cannot help but wonder if that is due almost entirely to the fact that he can give the team 180-200 IP. Corbin will be on a limit of 160-180 IP. Ray is unlikely to go over 160-180 (probably closer to 160). If the team lands Maeda, there is a fair chance he doesn’t break the 180 IP barrier either, since he’ll be working on shorter rest in a higher stress environment than he is used to right now.

    Personally, I move RDLR to the bullpen today and then slot Blair in to start the season, no need for service clock shenanigans. That would help the IP problem and also bolster the bullpen. I don’t see TLR having that sort of thinking in him though.

  6. […] residue in 2014 seems to have stuck to Marshall before or after that one season, which makes sense; line drive percentage is one of the least stable pitching statistics. That means that if the high line drive percentage was responsible for that unusually high BABIP, […]

  7. […] has made that look fluky by registering a 2.31 ERA (and 20.2% LD%) through 8 starts. As Jeff has explored, line drive percentage is very unstable year to […]

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