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. 

Thank you for reading

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I know where to find k/9 on a player page on BP but where do I find K%?
I think I still would rather go for the K/9 stat. I have a # that I think will win the Ks cat in my league this year. We also have an innings cap, of course. So, I have figured out a K/IP ratio that will be necessary for me to maintain to win the Ks cat, assuming I max out our allowed innings. This helps me make adjustments to my staff and decisions in who to make active. I now understand, after reading your article, that the K rate may help me in selecting the most effective strikeout pitchers when drafting, trading or acquiring free agents. One more useful tool in the belt never hurt!
I had 2 pitchers for a daily game I am playing today. Hamels vs the Pirates was a no-brainer given they're awful vs LHP but went with McAllister over Iwakuma today for two reasons. 1 - McAllister is tough on RH and the only LH threat in Chicago can't hit right now and 2 - the blister issue that has been around all season and chased him after 70 pitches last start. You sold me on Iwakuma in the off-season and I have him in 5 leagues including a second straight season in AL Tout.
I did not have a chance to watch the Astros/Mariners last night( Comcast still holding Astro games hostage), but Iwakuma struck out 11 of 25 batters(44%!!!) in only 5 innings, while burning 93 pitches to do it. Not terribly efficient, although the fact that he threw that many pitches might indicate the blister is no longer a big deal.