A glance at Iwakuma’s recent struggles

 It goes without saying: every starting pitcher, no matter how talented, is going to throw a clunker once in a while. Even the great Clayton Kershaw allowed seven earned runs in a May start against the Arizona Diamondbacks, though that’s really his only blemish in an otherwise terrific season. So, as good as Hisashi Iwakuma has been for the Seattle Mariners this year, there’s little doubt that one would be able to look back on the season as a whole and pick out a handful of starts in which the right-hander was less than stellar — which brings us to a conspicuous last two weeks of from the No. 2 starter.

On Wednesday night, the Mariners lost a very winnable game to the Houston Astros who’ve been riding a hot streak of late. Normally with Kuma on the mound a victory seems easily within reach, as long as the bats don’t forget to show up. However in this contest, the bats didn’t provide much help and Iwakuma gave up four earned runs in four and one-third innings of work. A lack of offense on any given night has been a regularity for the 2014 Mariners — though they’ve become more consistent as the season has worn on — but a fourth-straight poor outing from the right-hander? It would appear that perhaps something isn’t quite right.

Over his last four starts, Iwakuma has allowed 15 earned runs in 18 innings of work which includes an outing against the Washington Nationals in which he gave up three home runs, all solo shots — he had given up just 14 entering the game. His ERA over that period is a gaudy 7.50, but his 4.29 FIP and 2.96 xFIP suggest that he hasn’t performed as bad as his earned run average would suggest. That’s good news considering he only allowed four walks while striking out 18 batter during that stretch, and his 25 percent home run per fly ball rate is double the 12.1 percent rate he’s produced all season.

Naturally, we start to wonder if there’s some cause of Iwakuma’s struggles over this period considering how dominant he had been prior. It doesn’t appear to be a mechanical thing and there’s no reason to believe that the starter is batting any type of injury aside from the regular fatigue that comes in to play through the course of an entire season. Prospect Insider’s Jason A. Churchill wondered on Twitter Wednesday night if Kuma had been throwing more splitters than usual, and thanks to this chart via BrooksBaseball, we can see that in fact, he has increased his usage of the splitter over his last four outings.

  Iwakuma has now made 25 starts on the year and averages a tick over 91 pitchers per start. Of those 91 pitches, just under 25 are splitters on an average basis. Make no qualms about it, Kuma is a sinkerball pitcher and thus has relied on it about 35 percent of the time in 2014. His splitter is used about 27 percent of the time and just 13 percent of his pitches are four-seam fastballs as well. In his last four starts — the period in question — the 33-year old has utilized his splitter 34, 22, 32, and 39 percent of the time respectively, three of those four numbers would be considered above average within the context of this season.

Now, in Kuma’s August 14th start against Philadelphia he threw eight shutout innings and 27 percent of his pitches were splitters. On another instance during July against Oakland Iwakuma took a shutout into the ninth inning before yielding a two-run home run and used his splitter 26 percent of the time. There was also a start in June versus Texas in which the right-hander allowed one run in eight innings of work while relying on his splitter for 34 percent of his pitches — several percentage points higher than his season average.

[pullquote]Iwakuma has mixed in a cutter at various points in the season for the first time in his career. He’s thrown it no more than six time during a single start and many it isn’t used at all. Kuma has also utilized his curveball less in 2014 than he has in the past.[/pullquote]

The thing that makes a splitter effective is that during delivery, it should appear practically identical to the delivery of a four-seam fastball — the difference, obviously, is that the splitter will break several inches and in some instances be a couple ticks slower than the fastball. As mentioned, Iwakuma relies heavily on his sinker and on only three occasions this season thrown it fewer than 30 percent of the time. In the first half of the season Kuma was using his splitter about 26 percent of the time compared to 29 percent in the second half, so he had started to utilize it more frequently earlier than just this recent stretch. Although the reality is that on average it’s only a couple more times each outing that he’s actually throwing the pitch.

It’s tough to really make much about a few starts worth of data in relation to why Iwakuma’s production numbers are down. For what it’s worth, in his first two years in the majors he threw a splitter approximately 22 percent of the time so the 27 percent usage thus far in 2014 is an increase, but it isn’t as if it’s significant. For context, out of every 100 pitches the right-hander throws, five more have been splitters in 2014 compared to 2013.

Perhaps the more interesting factor, which Churchill also mentioned on Twitter, is Iwakuma’s use of his four-seam fastball. Naturally sinkerball-pitchers rely heavily on their sinker or a two-seam fastball, but it’s curious to note that the right-hander has thrown four-seamers just 13 percent of the time so far this year which is a fairly substantial drop from the 28 percent mark in 2013 and 30 percent mark in 2012. It’s common for pitchers to set up their splitter with a four-seamer since, as mentioned, the mechanics of both pitches are very similar.

Perhaps Iwakuma’s decreasing fastball use is more concerning than his increased splitter use, but at the end of the day, we’re still dealing with too small a sample size to make much about. The decreasing fastball use is interesting because it’s occurred over a few years now, but it’s typical for pitchers to stick with what’s working. If Kuma feels his splitter is his best pitch on a certain night, naturally he’s going to stick with it. Same for his fastball, sinker, curve, or slider. But it’s rare that a pitcher cuts their four-seam usage by half within a year’s time.

Whatever the case, Kuma has seen a spike in his BABIP over this four-start stretch — a .375 mark compared to the .284 he’s put up on the season. Could we point to the fact the right-hander has simply given up more hits and been slightly unlikely over the last couple weeks? Certainly. It’s not as though he’s had noticeable control problems and although his walk rate doubled in that period, it’s still the second lowest in all of baseball.

Iwakuma will be fine as this appears to be no more than simply a rough patch. The use of his fastballs is fascinating, but it’s difficult to draw many conclusions without more data to crunch. For all we know, the right-hander could throw eight shutout innings while using his splitter 40 percent of the time during his next start.

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