A Hidden Problem with Bronson Arroyo

The Diamondbacks signed Bronson Arroyo to a two year, $23.5 million contract on Friday, and predictably, response from the statistical community wasn’t that positive, especially with Paul Maholm signing for just $1.5 million in guaranteed money with the Dodgers earlier in the afternoon. Jeff already wrote up the pros and cons of Bronson Arroyo’s deal this morning, which I’m essentially in agreement with, so feel free to read that if you’re just looking for a summary of the deal. However, there’s another aspect to Arroyo that I think is worth mentioning, especially considering that he’s changing divisions.

Arroyo has really large platoon splits; some of the largest in the game, in fact. Over the last three years, he’s held RHBs to a .290 wOBA, much better than the league average, but LHBs have put up a .374 wOBA against him, making him one of the worst regular starting pitchers in baseball against left-handed bats. Among right-handed pitchers who have faced least 1,500 total batters over the last three years, only Jason Marquis (.389 wOBA) has been worse against left-handed bats. Including LHPs (which brings in the disastrous Ricky Romero), Arroyo ranks 106th out of 108 starters in wOBA vs LHBs since the start of the 2011 season. It’s a pretty big flaw.

Now, it’s not that uncommon for a pitcher to strongly favor pitching to same-handed hitters, and he’s hardly the only starter with a big platoon split. Gavin Floyd and Justin Masterson actually have bigger ratios between their wOBAs against lefties and righties, and Max Scherzer, Rick Porcello, and Lance Lynn aren’t far behind. These are all pretty solid pitchers — Scherzer obviously is more than just solid — and shows that a big platoon split doesn’t ruin a RHPs chance of sticking in the rotation. After all, you only have a big split as a Major Leaguer if you’re particularly good against same-handed hitters, so we’re selecting for pitchers who are strong against one side, giving them the ability to get some hitters out with a lot of frequency.

But this also leaves them vulnerable against teams who can stack the deck with lefties, and pitchers who run big splits tend to face a lower percentage of same-handed hitters than pitchers with a more even split. For reference, here are the five RHPs with the biggest platoon ratio over the last three years, with their batters faced totals included as well.

Player VsRHB VsLHB Total Platoon% RHBwOBA LHBwOBA Platoon Ratio
Gavin Floyd 722 910 1632 56% 0.274 0.356 1.30
Justin Masterson 1078 1539 2617 59% 0.259 0.335 1.29
Bronson Arroyo 1246 1267 2513 50% 0.290 0.374 1.29
Rick Porcello 1032 1271 2303 55% 0.291 0.369 1.27
Max Scherzer 1059 1397 2456 57% 0.264 0.334 1.27

Notice Arroyo’s Platoon%, relative to the other four? Masterson has faced nearly 60% lefties, and Floyd and the two Tigers are both over 55%. Arroyo, though, is at just 50%, as he’s faced an almost identical number of right-handed and left-handed bats since the start of the 2011 season.

A big part of that is that he’s the only National League starter in that group. An AL manager is never going to put a right-handed DH in the line-up against these guys if they can help it, so there’s basically an extra left-handed bat in the line-up against the AL platoon guys every single time out. It’s simply easier for AL managers to exploit platoon splits than it is for NL managers, which is one of the reasons why pitchers like Arroyo have more success in the NL than the AL.

But it’s not just the National League factor pushing Arroyo’s ratio of left-handed hitters down. It’s also the National League Central factor, and maybe even more specifically, a Cincinnati Reds factor. The Reds themselves had a decent amount of left-handed hitting last year, ranking 3rd in the NL in PAs from LHBs, but of course, Arroyo didn’t have to pitch against his own team, and the rest of the NL Central teams simply didn’t have much in the way of left-handed hitting.

The Cubs and Cardinals ranked 6th and 7th in the NL in PAs from LHBs, while the Pirates ranked 13th and the Brewers ranked 15th. The Brewers, in fact, were on an island to themselves in terms of right-handed slant, as every other NL team had at least 2,000 PAs from LHBs in 2013, while the Brewers had just 1,690. The Phillies and Giants sent nearly twice as many left-handed hitters to the plate last year as the Brewers did.

This wasn’t just a one year fluke, either. The non-Reds NL Central teams ranked 6th/9th/10th/11th/15th in LHB PAs in 2012, and 7th/9th/12th/13th/16th in 2011. For whatever reason, the NL Central has just not had many left-handed hitters over the last few years, with nearly every team skewing to the right side of the plate. So perhaps it shouldn’t be a huge surprise that other high Platoon Ratio/Low Platoon% pitchers happen to pitch for NL Central teams as well. Charlie Morton (PIT) has had a whopping 1.44 Platoon Ratio, but just 46% of his batters faced have been LHBs. Lance Lynn (STL) posted a 1.26 Platoon Ratio, but only faced 46% LHBs over the last three years. Shaun Marcum (MIL, mostly) put up a 1.24 Platoon Ratio, but faced just 49% LHBs from 2011-2013. Jeff Samardzija (CHC): 1.14 Platoon Ratio, 47% Platoon%.

Outside of NL Central hurlers, we just don’t really see examples of righties who struggle against lefties getting to face more righties than lefties. Especially in the AL, these pitchers end up facing 55-60% LHBs, and even in the NL West and East, the number is more regularly in the 52-53% range. And unfortunately for Bronson Arroyo, he doesn’t get to take the NL Central’s distribution of hitters with him to Arizona.

How big a deal is a few percentage points in platoon distribution? Well, let’s use Arroyo as an example. If you just take his three year wOBA against numbers (.290/.372), here’s what his total wOBA allowed would look like based on different platoon ratio distributions.

50/50 PA wOBA
RHB 425 0.290
LHB 425 0.374
Total 50% 0.332
—- —- —-
45/55 PA wOBA
RHB 380 0.290
LHB 470 0.374
Total 55% 0.336
—- —- —-
40/60 PA wOBA
RHB 340 0.290
LHB 510 0.374
Total 60% 0.340

You take the same pitcher with the same skills and move him from a 50/50 to a 40/60 distribution, and his wOBA allowed goes up eight points just from the additional number of left-handers he’d have to face. Eight points of wOBA might not seem like a big deal, but over 850 batters faced, that adds up to about an extra six runs allowed per year. Over 200 innings, that’s roughly equivalent to 20 points of ERA.

Now, Arroyo almost certainly won’t face 60% left-handed hitters in Arizona, since it’s still an NL team and he won’t have to face DH-filled line-ups too often, but this is one of those subtle things that suggests that Arroyo’s change of location might make him a little worse off than even the modest projections already suggest, and perhaps more importantly, this flaw significantly limits Arroyo’s usefulness in October. While there’s an argument to be made that regular season totals understate the importance of frontline pitchers and ace relievers in the playoffs — which is likely one one the reasons why teams pay premiums to acquire these types of players — starters with big platoon splits are less valuable in October than they are in the regular season.

If Arizona happens to make the postseason, any team facing them in the NLDS or NLCS will have the ability to stack its roster in such a way as to force Arroyo to face a bunch of left-handed bats, and if Arizona makes it to the World Series, starting him in an AL park is basically a no-go, because otherwise he’d be tasked with facing yet another left-handed bat in the form of the DH. In other words, the Diamondbacks paid Arroyo $23.5 million to help them make the playoffs in the next two years, but if they get there, he probably won’t be able to actually help them much in the postseason, given that his success is pretty dependent on facing line-ups filled with right-handed hitters.

This isn’t just a warning for the Diamondbacks. This is relevant for any team trading for Samardzija, Lynn, or any other right-handed pitcher in the NL Central. It’s not a huge factor and shouldn’t be the reason why you don’t complete a trade for a hurler from that division, but it’s worth keeping in mind that the RHPs in the NL Central are probably not quite as good as they look.

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Dave is a co-founder of USSMariner.com and contributes to the Wall Street Journal.

26 Responses to “A Hidden Problem with Bronson Arroyo”

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  1. DrBGiantsfan says:

    Not sure why you would call this a “hidden” problem. Isn’t Arroyo’s extreme platoon split quite well known?

    This is why I was intrigued by the thought of him signing signing with the Giants, because AT&T Park absolutely crushes LH power.

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    • danlby says:

      The platoon split is not hidden, but the NL Central’s LHB/RHB split (particularly outside of Cincinnati) is news to me.

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  2. Mookywilson says:

    Thanks Dave.
    This is good stuff right here–why I read Fangraphs.

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    • Bip says:

      Another reason I read fangraphs: Dave doesn’t end the post with “therefore the diamondbacks are dumb and this is the worst signing ever.” Articles on this site will typically assess different strengths/weaknesses of a move without feeling the need to tie the piece into a larger narrative about the intelligence of the franchise (unless it’s the Royals, I guess.)

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  3. walt526 says:

    I think you have to regress his platoon splits some if you’re going to project what he’s doing 60/40 rather than 50/50. Part of the reason why he extreme platoon splits might be the relative small sample size.

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    • Ian R. says:

      Arroyo has had pretty significant platoon splits throughout his career, though. RHB have posted just a .680 OPS against him lifetime, compared to .834 for LHB. He’s also the sort of pitcher you’d expect to have a problem with opposite-handed hitters – he doesn’t throw all that hard, his best pitch is a sweeping curveball, and he also throws a slider.

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      • Bip says:

        I think curveballs tend to have reverse splits. Sinkers and sliders tend to have the biggest normal splits.

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        • Dag Gummit says:

          As far as I knew, the general rule with a particular pitch’s platoon split (over the whole of all pitchers that use it) is the direction of its movement. As a rule, batters did worse with pitches that break away from them and better when they break in.

          From that, it always seemed that sliders, curves (especially sweeping varieties of both) and most two-seam FB varieties would have the biggest platoon splits. In contrast, changeups, splitters and forkballs would more frequently have reverse splits. Curves and sinkers in particular could potentially have a strong split or be neutral because they can either break (mostly) vertical or across depending on the grip and arm motion.

          I have to admit, though, that I’ve never seen or heard of any study on platoon splits of particular pitches. it would be interesting to look at not just classified pitch types but also breaking things down into direction and amount of movement.

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    • Schlom says:

      Correct me if I’m wrong but I thought that Dave (in either another post or maybe a chat) said that extreme platoon splits aren’t real and have to be regressed. If that’s true this post is at odds with that view.

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  4. Leroy says:

    Dave, is it correct to conclude that some NL Central hurlers are underrated for the same reason?

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    • Bip says:

      Sure, if you can show that NL Central LHP face more RHB than do LHP in other divisions, that might be a reason to give them a bit of a bonus if they leave that division.

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  5. Bip says:

    Here’s the part where I point out that Clayton Kershaw, a lefty, has a lower wOBA allowed against RHB than anyone else except Strasburg – who has the same wOBA allowed – in way more RHB faced. Crazy.

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    • walt526 says:

      Part of that is an artifact from selection bias: the lefties that Kershaw sees are generally the very good ones or those who don’t display much of a platoon split.

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      • Bip says:

        That does not relate to the split I mentioned, though I see how it would apply the other way around: i.e. teams are more likely to sit their bad RHB against a RHP, so Kershaw is more likely to face bad RHB and good LHB, whereas a RHP will tend to face better RHB and worse LHB. Generally though, we don’t expect that effect to counteract a pitcher’s platoon split.

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  6. Yes, it is true that we would expect x number of players to outperform there peripherals based on randomness alone. But we also know that there are a lot more pitchers that outperform peripherals than randomness would expect.


    So we know that skill exists. So what should we do with it? Regression, of course.

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  7. Oops wrong thread. Nevermind.

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  8. Biesterfield says:

    Nice article. I checked to see if the QUALITY of LHB Arroyo faced was lower than usual, in addition to the QUANTITY, as you have shown. Turns out, this was not the case, largely due to the Cardinals great LHB and switch hitters.

    OPS when batting left handed, 2013:
    AL East: .760
    NL Central w/ Reds: .753
    NL Central w/o Reds: .732
    AL West: .722
    AL Central: .721
    NL West: .701
    NL East: .698

    Also of note, NL Central’s LHB are much better than their RHB, even after taking CIN out.

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    • Ian R. says:

      Now, that’s interesting. It also looks like the effect of leaving the Central will be somewhat counteracted by the lower quality of LHB in the NL West – though I suppose it might be different if you take out Arizona’s hitters.

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  9. shthar says:

    Back when teams carried 10 pitchers, you could platoon at more positions.

    If you got 13 pitchers, you can barely do it at all.

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  10. MGL says:

    Excellent perspective, Dave!

    Yes, it is true that one must regress his splits the appropriate amount when doing a “What if?” analysis. Keep in mind that when one regresses observed splits toward league average splits for that handedness, that one can use a different mean to regress toward based upon a pitcher’s arm angle and his repertoire. For example, a pitcher who uses predominantly sinker and slider will have a higher “natural” split than one, who uses, say a change-up, curve ball, and 4 seamer. In fact, I have a regression formula that I use to establish the mean toward which I regress a pitcher’s splits, where the various pitch frequencies are the independent variables.

    Finally, Dave is being a little dramatic and overstating the effect (to be generous) by declaring that he will not be particularly useful against an AL team in the playoffs just because they CAN use a LH DH. First of all, at most, it is ONE extra LH batter in the lineup. Second of all, many teams are NOT going to change their usual RH DH if they have one. Third of all, if a team does decide to bench their regular RH DH in favor of a LH DH, he will not as good overall as the RH DH, do the gain against a RH pitcher with large splits will be small. Fourth of all, the last time I looked you face the same league in the playoffs (unlike the regular season, where every 15th game or so is an inter-league game) until the very last round (the WS).

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