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.