What You Didn’t Know About Hisashi Iwakuma

Very late last week, another quality starting pitcher in Hisashi Iwakuma nearly entered the free-agent market. But very late last week, the Seattle Mariners decided “hey we need quality players on our team” and re-signed Iwakuma to a multi-year contract. It was a predictable move, and a sensible move; the Mariners needed a good starting pitcher, and Iwakuma had previously expressed a fondness for Seattle. The two sides reached an agreement right at the end of the exclusive negotiating window, and Iwakuma will end up with either $14 million over two years or $20 million over three years. For the Mariners, it’s a potential bargain, and for Iwakuma, it’s security and still a small fortune.

Now, as for the headline, in your case the answer might be “literally anything.” Iwakuma last year flew under the radar, because he pitched for a nothing team, and he didn’t actually start pitching regularly for a few months. For me, personally, Wei-Yin Chen is a blind spot. For a lot of other people, Hisashi Iwakuma might be a blind spot. I don’t know. One should first acknowledge that he was pretty good. Then there’s something else, something specific.

Let’s be real here: the Mariners re-signed Iwakuma for such an affordable price presumably because of his previous shoulder troubles. Iwakuma missed time in Japan in 2011 because of his shoulder, and though there weren’t any signs of problems in 2012, shoulder problems aren’t forgotten that easily. By performance, Iwakuma was anywhere from “average” to “really good”. Beginning on July 2, Iwakuma made 16 starts for the Mariners. He posted 78 strikeouts against 28 walks, and his first two starts might’ve been his worst.

We’re throwing away Iwakuma’s bullpen performance because Iwakuma isn’t a reliever, and because his usage pattern was sporadic. As a starter, he posted a lower ERA- than Chris Sale, the same FIP- as Yovani Gallardo, and a lower xFIP- than Hiroki Kuroda. By FIP, Iwakuma was average, and by xFIP he was better than that, and while Iwakuma might have a home-run problem, over samples like his we have to regress heavily. We don’t yet have compelling reason to believe that Hisashi Iwakuma is unusually homer-prone.

Depending on how you look at things, on a per-inning basis Iwakuma out-performed or at least equivalently-performed Anibal Sanchez. Sanchez is one of the prizes of the free-agent market, and he’ll sign for more guaranteed money than $14 million over two years. This is why Iwakuma is not a certain bargain, but a possible one.

So what is it about Iwakuma that makes him effective, specifically? Truth be told, it’s a blend of things, as it usually is. He throws enough strikes, he misses enough bats, he gets enough grounders. Overall, Iwakuma is outstanding in no one category. Things just come together. But Iwakuma does have a signature weapon. This is where we really get into something you didn’t know, because this is something I didn’t know before I went to the numbers.

Iwakuma throws a splitter, see, and he throws it kind of a lot. That isn’t an unusual pitch, especially for a Japanese starter, but what makes it more unusual is the success. According to Brooks Baseball, Iwakuma threw his splitter roughly a fifth of the time, and it yielded 72 grounders, 13 line drives, and seven fly balls. That’s a 78-percent groundball rate. It also yielded zero home runs, mostly because the balls in play weren’t in the air for very long.

Let’s take a trip to the PITCHf/x leaderboards. Out of all the pitches that a starting pitcher threw at least 200 times — and there were an awful lot of them — not one yielded a higher groundball rate than Iwakuma’s splitter. If you look at relievers, Iwakuma’s splitter comes up just shy of Craig Kimbrel‘s curve and Brad Ziegler‘s fastball, but one should be wary when it comes to comparing starters to relievers and clearly, Iwakuma’s splitter is a grounder-heavy pitch. Here’s a .gif of it, because there’s nothing wrong with having a visual:

Okay, let’s continue. Iwakuma threw his splitter for a strike two-thirds of the time. Iwakuma also favored his splitter in pitcher-friendly counts, implying that he threw a lot of splitters out of the zone. Texas Leaguers confirms:

That pitch, with that location pattern, generated two-thirds strikes. Reason? According to Brooks Baseball, Iwakuma’s splitter generated 14 called strikes and 262 swings. Even if the specific numbers are a little off, the ratio will hold true. Iwakuma’s splitter got strikes not because it was freezing hitters, but because it was doing the opposite of that. Iwakuma’s splitter got strikes because it was burning hitters?

Here is another visual, because yay visuals!

There’s nothing real remarkable about Iwakuma’s fastball. He has a broad enough repertoire, though, to get ahead in the count with regularity, and when Iwakuma is ahead he goes to his splitter more often, and Iwakuma’s splitter is the underrated sort of lethal. It entices batters to swing at it, even though it’s often located out of the zone. When batters swing, they will often hit the ball on the ground or miss the ball completely. Even if hitters have a pretty good idea that a splitter is coming, it spends enough time in the strike zone that they often have to protect, and that’s when Iwakuma thrives.

Statistically, Hisashi Iwakuma looks like a pretty good starting pitcher. And with the splitter, he’s a starting pitcher with an out pitch, which makes his success seem all the more sustainable. It’s a weapon that he’s got in his back pocket, and it’s a weapon that even I didn’t realize was quite this potent, and I watched Iwakuma all year long. Next season will bring greater familiarity and more advance scouting, but as long as Iwakuma mixes things up enough, his splitter should be able to carry the mail. I don’t actually know what that expression means, but it feels right.

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Jeff made Lookout Landing a thing, but he does not still write there about the Mariners. He does write here, sometimes about the Mariners, but usually not.

26 Responses to “What You Didn’t Know About Hisashi Iwakuma”

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  1. Eric Dykstra says:

    I wasn’t at all surprised that Iwakuma ended up back with the Mariners, but I wonder why FAs-to-be so often re-sign with the same team. Any particular reason Iwakuma decided just to go with the Mariners than to test the waters with 29 other teams? Or Oliver Perez? Do they just think the Mariners will give them more than any other team? Why are the Mariners willing to make an offer so high that the players would not want to even hear offers from 29 other teams?

    I don’t really get it… I think it’s a fair deal, maybe a slight bargain for the Mariners.

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    • D.t. says:

      Maybe he was just happy there and knew that the Ms knew how to make Japanese players comfortable, something other teams don’t have nearly as much experience with.

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    • Jason says:

      His wife and two children live in Seattle.

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    • Daven says:

      Had he not re-signed with the Mariners on the day he did, he wouldn’t have been able to pitch for them until May 15th, if he later chose to sign (it was a stipulation in his original contract that they release him if they didn’t sign him by the date they did, which makes him ineligible to play for the Mariners until May 15th, if I recall correctly).

      Had that not been the case, he of course would have been smarter to test the market, even if he was going to sign with the Mariners all along, just to see if he could up his contract a bit.

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    • David G says:

      Who’s going to give him more money and give him a better city to live in?

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  2. Scott G says:

    Good Stuff. I had taken Iwakuma in a few AL leagues but had to drop him since the first few months he was hardly used . I don’t recall if Seattle stated what the reason was for holding him back, since he was active

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    • D.t. says:

      Officially he wasn’t fully recovered from his shoulder issues. Unofficially, Wedge hasn’t got a clue when it comes to evaluating talent and judged him off of his bad spring numbers.

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      • Scott says:

        Is Wedge the reason why Jaso didn’t get much playing time in the beginning of the year? If that’s the case, that’s a pretty awful trait for a manager.

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      • Basebull says:

        It’s fun to speculate, but I think it’s just as reasonable to believe that they didn’t think he could adjust to the five-man rotation and wanted to ease him in – something that could have contributed to his success later in the year. Wedge and the front office deserve to be raked over the coals for plenty, but I’m not convinced that this counts.

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      • Gary York says:


        Yes, Wedge was the reason that Jaso did not play much early. Wedge has a great fondness for Miguel Olivo, so much so that sometimes he actually DH’d him, a fairly indefensible move given that Olivo ended up with an OPS somewhere in the high .500s. If Jaso hadn’t gotten hot in a pinch hit and occasional start role, he’d still be sitting on the bench (figuratively–they wouldn’t have made him stay in Seattle to sit on the bench after the season was over. At least I hope not.)

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      • Daven says:

        @Scott: Yes, Jaso also road the pine for a good percentage of the beginning of the season. Funny that the Mariners started being OK when those two started to get to play regularly, rather than guys with “veteran grit”. Wedge’s roster decisions, particularly as he seems to take a lot of stock in what a player does in Spring Training and how much “veteran grit” they have, has made me anti-Wedge, and I’m rarely anti-manager, just because I usually like to give them the benefit of the doubt, as they have far more information available than we do on players and day to day stuff like bumps and bruises and the like.

        Can’t wait until Wedge gets fired (obviously he will at some point, as pretty much all coaches / managers / GMs do).

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    • Kazinski says:

      Iwakuma started the season with a pretty bad condition that a lot of players just breaking into the big leagues never recover from: Retarded Manager.

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  3. Casey McLain says:

    The Mariners had an exclusive negotiating window that lasted longer than the standard window for free-agents-to-be, but as a result, they were subject to the same set of guidelines as if Iwakuma was a player they’d non-tendered in that if he signed with them he wouldn’t have been able to pitch until May 15. Similarly, if Iwakuma opted against signing the Mariners contract he likely had zero chance of returning, as being certain to lose a month-and-a-half of a pitcher is very unlikely to make a team increase their offer.

    And to Scott, Iwakuma had some shoulder issues in Japan and apparently had some issues adapting to the conditioning schedule of the American game.

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  4. Sage, 12 yrs old says:

    Yeah, I’ve known about his awesome splitter since he was in Japan. I wanted to see him in the Majors because I knew he could get so many ground balls. It’s great that the Mariners got a solid No.2 or 3 guy, because the Mariners starting pitching was falling short sometimes. Yay Iwakuma and yay for smart Mariners!

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  5. Name says:

    “This is where we really get into something you didn’t know, because this is something I didn’t know before I went to the numbers.”

    You should read Seattle Sports Insider more. Jemanji called it in January.

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    • He called the highest groundball rate among starting pitchers in baseball?

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      • ThirteenOfTwo says:

        Kind of. He called an extremely high ground ball rate. Talking about Iwakuma’s split (or, as it’s called in Japan, the shuuto):

        “ML hitters will make contact with this pitch, usually, but they will two-bounce them to third base. Check Fangraphs’ data on the shuuto. 325 shuutos in 2010, of which 53 were groundballs, and only 14 fly balls. You tell me. How do you hit this pitch in the air?”


        That article. Dude’s pretty perceptive.

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      • marc w says:

        To 13 of 2
        That article says it’s the two-seamer/shuuto that would generate a ton of ground balls. He can’t be talking about the split, because the article also notes a forkball, and it’s clear from the pitch fx chart there which one is which.

        As it happens, Iwakuma does have a 2-seamer, and it generated some GBs, as most 2-seamers do. But he’s clearly not talking about the split, which is slower and has more sink.

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  6. steve says:

    TWO entirely unnecessary paragraphs to start the article this time! You’re really stepping up your game, Jeff ;)

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  7. Name says:

    Here he talks abut the splitter
    “Q. So who are Iwakuma’s comparables?

    A. He is in the Mussina / Cone family, but red-shifted towards ground balls. None of these other guys throw a GB-happy Shuuto. Also, Iwakuma’s splitter induces a bizarro GB ratio, and even the FB gets topped. Iwakuma’s GB ratio is over 2:1.”


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