As of Friday, Iwakuma has left 100 percent of batters on base through four starts in 2013. That mark seems pretty impressive until you realize that all of his earned runs have come as the result of home runs. Right now Iwakuma has an ERA of 1.69 and has struck out almost twenty percent of batters faced while walking just over two percent-he's doing well fooling hitters with his breaking pitches.
Even lower is Iwakuma's BABIP of .119 which further demonstrates the burn of the aforementioned home runs. Iwakuma had a below average BABIP last year though we don't have enough historical (MLB) data on him to determine if we can expect more of the same.
Whats concerning right now is over forty-two percent of his hits are fly balls and over thirteen percent of those have ended up home runs. Three of the four have come on the road and you'd have to assume that if most of Iwakuma's starts are at Safeco that--even with the fences moved it--his HR/FB rate will have to come down.
Iwakuma has been more of a ground ball-type pitcher through his career (in both the US and Japan), relying on breaking pitches to get those results. Right now, his ground ball rate is just above twenty-seven percent. That's actually pretty good for a 'normal' pitcher, but slightly worrisome for a ground ball pitcher. That could mean that he's leaving too many breaking pitches up in the zone which can be incredibly dangerous. He's throwing a sinker on just over twenty-three percent of his pitches and its being put in play 32.9 percent of the time-the only other pitch that comes close to that rate is his split finger at 19.6 percent contact.
That being said, his fastball is thrown the most and has also gotten him in the most amount of trouble. A pitcher like Iwakuma should use that pitch as a 'throw-off' pitch but instead it has become a meatball. Right now, if you look at his fastball runs above average (wFB), it sits at a 3.8 which is not bad but much higher than his other pitches. Also, his fastball velocity is down slightly from 90.3 to 89.7. Not a major shift but slow enough for fastball hitters to get a strong swing on.
As you can see, most of his fastballs are falling dead middle in the strike zone:
Since his nastier pitches--the breaking balls--are his bread and butter, all a power hitter needs to do is wait for his fastball and swing away. Right now, less than 10 percent of his fastballs swings have been whiffs.
If Iwakuma can get back on track and reverse his fly ball and ground ball numbers, the home runs he's giving up can continue to be relatively harmless in spite of the luck he's having on the contrary. If he can generate better break and keep hitters off-balance with his fastball, he's in for a good season. However, it could end up being only be a matter of time before the unsustainable turns into the unimaginable for Iwakuma.