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Hisashi Iwakuma’s curveball was really bad in 2016

A look at what happens when good pitches go bad

Oakland Athletics v Seattle Mariners Photo by Otto Greule Jr/Getty Images

Hisashi Iwakuma’s surprise return to the Seattle Mariners was one of my favorite moments of the offseason. The idea of him wearing a Los Angeles Dodgers uniform never felt right, but it was happening. This much I knew was true after he signed a 3-year, $45 million deal to don the Dodger blue in the bright lights of SoCal. Then it all fell apart: medical concerns led to the Dodgers axing the deal and seconds later, Dipoto was at a team holiday party announcing that Iwakuma would be a Mariner in 2016 (with vesting options in ‘17 and ‘18, but no one really wants to enjoy their gin and tonic with a side of messy contract details).

It was a wonderful moment, but it also ended up being a crucial one: Iwakuma was one of the few pitchers who managed to avoid the disabled list. In a year where the Mariners were forced to throw multiple awful pitchers, Iwakuma stayed relatively healthy enough to prevent his annual trip to the list of the weak and the wounded. And yet, his year was a bit of a disappointment:

2016 was a down year in nearly every category for Iwakuma. Strikeouts were down, walks were up. He gave up more hard contact than he ever has before. His xFIP was a career worst by more than half a run. His ground ball percentage dropped nearly 10% from last year to now. I could go on, but I think we get the point now. Iwakuma wasn’t Iwakuma in 2016. That is the point I am making. You get it.

“IS HIS VELOCITY OKAY?” is the first question that pops into my brain in these situations. I recognize there are numerous things that can cause someone to have a bad season (which, hey, we’re about to get to), but velocity is usually one of the easier things to look into, so I tend to default to that as a starter. So, let’s look at Iwakuma’s velocity over the last three seasons:

Aside from the occasional off month, I wouldn’t say the velocity is down an earth shattering amount anywhere else but his cutter. And considering his cutter usage was close to nonexistent before 2016, I won’t put too much stock into it. Going strictly off his yearly averages, the most drastic of drop-offs from 2015 to now is seen in his curveball, which diminished from 72.35 mph to 71.31 mph. Since I remember his curveball being a pretty damn good pitch in 2015, let’s take a quick, closer look at that, using both Fangraphs and Brooks Baseball:

The pitch behaved differently and, interestingly enough, experienced a complete and total dismantling of its value. In 2015, it graded out as his best pitch. In 2016, it graded out as his worst pitch. For those that read my James Paxton piece last week, we are dealing in polar opposites here.

With Paxton, he adjusted to his newfound success with his cutter by throwing it more than ever. Surely Iwakuma recognized how ineffective he was with his curveball and adjusted by throwing it less, right?

Awesome! Not only is Iwakuma throwing his curveball worse than ever, he is now throwing it more than ever. And to put the icing on the disgusting, carrot-filled cake, here’s a look at how well he located these curveballs over the last two seasons:

The graph on the left shows 2015. He was terrific at keeping the curve either on the edges of the zone or below it, never leaving it up for a batter to drive. In 2016, he was all over the place with the pitch, so much so that I had to check numerous times to make sure I had entered the correct specifications for each graph. When you look through each zone individually, it may not seem like he was leaving pitches up significantly more, but he did so enough that you can understand why the opponent batting average against the pitch skyrocketed from .188 in 2015 to .328 in 2016. Could some of it have been simple BABIP luck? Of course, but the drastically different zones have to account for some amount of that gap. This also could account for the big drop-off on the amount of whiffs he generated on the curve, as displayed above.

Look, he is still only throwing the pitch <10% of the time, so it’s not like this curveball ruined his season. This is not the claim I am making. There were multiple other things wrong with Iwakuma in 2016. The fastball wasn’t as sharp, the slight velo drop across the board may have added up to something bigger, and the command issues aren’t limited to his curveball.

It is something, though. He leaned on the pitch more than ever, a trend that could continue into 2017, despite it generating poor results on a fairly consistent basis. It’s something to look out for next year, and something that could go a long way in determining whether he manages to get back on track or not. Here’s hoping he rediscovers that soft, bending loop that drops ever so sharply into the dirt (and not, you know, the middle of the plate). And should he not rediscover it, let’s hope he stops throwing it every tenth pitch. Either–or, Kuma, either–or.