Hisashi Iwakuma had the odd occurrence in his 2012 season where he was actually better as a starter. Most pitchers are not only better in short bursts out of the bullpen, but markedly so. Iwakuma spent 30 1/3 in the bullpen pitching to a 4.75 ERA and 1.42 WHIP with an 18 percent strikeout rate and 12 percent walk rate. He took off once he become a starter, posting a 2.65 ERA and 1.23 WHIP in 95 innings with a 20 percent strikeout rate and seven percent walk rate.

His 2013 season is off to an even better start as he has managed a 1.69 ERA and 0.53 WHIP in 26 2/3 innings through his first four starts. The only impediment to his success so far has been a blister issue, though something tells me his 100 percent left on base rate and .119 BABIP are set to rise. I have noticed that his batted ball mix is different from 2012 as his flyball rate climbed dramatically from 27 percent to 42 percent, including a 13 percent infield flyball rate.

However, that isn’t my focus today (though it bears further examination should it continue). I’m more intrigued about what Iwakuma has done in a particular pair of stats that purport to measure roughly the same thing, though one is markedly more effective than the other. And Iwakuma’s early season work is just the case study to use to illustrate the vast difference.

It wouldn’t be outlandsih to see something written of Iwakuma highlighting his early season success and addressing the batted ball mix differences I mentioned while also including something to effect of “he has done all of this despite striking out fewer batters than last year with a 6.1 K/9 compared to 2012’s 7.3 mark.”

I have recently grown quite fond of strikeout percentage. I wrote an essay about in the front of this year’s Starting Pitcher Guide on why I prefer it to K/9 and why it is a better indicator of a pitcher’s true ability to miss bats. It isn’t like going from batting average to on-base percentage where the latter can show exceptional value in cases that the former failed. I said as much in the SP Guide: “The point isn’t that K% is going to unearth hidden sleepers that everyone was overlooking. Rather, it is offering an incremental step forward toward a better understanding of pitcher efficiency.”











Remember the mock-analysis from above? Turns out it would be 100 percent incorrect. If you are currently using K/9, make the switch to K% and you will instantly improve your understanding of a pitcher’s performance, if only incrementally. As long as you have a batters faced count, you can easily figure out strikeout percentage (simply divide the strikeouts by the batters faced). It isn’t usually in the line score for pitchers, but often just below as you can see here in the examples of and boxscores.

Iwakuma has a chance to further improve his strikeout percentage tonight when he faces the Houston Astros who “lead” the majors with a 26.3 percent strikeout rate. They are 26th in walk rate at 6.8 percent.