What is the deal with Nate Cornejo

Nate has made three starts this year. The first he pitched well enough to pick up the win. The next two starts were atrocious. Cornejo’s ERA is currently sitting at 9.73 and he’s allowed 36 baserunners in 16 1/3 innings. Last year Cornejo was fairly effective despite a cosmically low strike out rate. I decided to take a look at some of his rate stats this year, and see how they’ve changed.

The good news is Cornejo has doubled his strike out rate. The bad news is he has doubled his home run rate, and increased his walk rate as well. The number that really gets Nate into trouble though is his batting average on balls in play (BABIP). When hitters aren’t strking out, hitting homers, or walking, they are dropping hits on Nate at a Ted Williams-ish rate. The result is 17 runs in three appearances.

The good news is that there is a whole school of thought out there that would theorize that Cornejo has actually been unlucky and not just bad. There has been some extensive analysis performed by people way smarter than me, that shows that pitchers have limited to no ability in preventing hits on balls in play. That being said, given that Cornejo has been unlucky so far it wouldn’t be unreasonable to expect a regression to the mean over time.

Last year the Tigers were pretty close to an average defense in terms of allowing hits on balls in play. The league average was .291 and the Tigers average was .296. Nate Cornejo’s average was .303 which was slightly higher than the Tigers average, but not significantly so. While I haven’t been able to dig up similar stats yet this year, one would expect league numbers in the same range, and there is a widely held belief the Tigers are better defensive this year than last year (which probably is justified). If that’s the case, one would expect Nate’s current .412 number to start to approach something in the .290′s to low .300′s.

As further proof that these numbers can fluctuate, Cornejo had a similar “slump” last year when he had a month and a half of starts where his BABIP was .400.

However, Nate had one other thing working for him last year. He had a high double play rate. The league average was a double play in about 13% of opportunities. Cornejo’s rate was 19.3%. Given the large number of opportunities last year, that equates to 11 more double plays than would be expected. Given the limited ability pitchers have in turning balls in play into single outs, I’d expect that pitchers exert even less control on turning balls in play into two outs.

So what does all this mean? My take is that things will get better for Cornejo this year. The fact he has double his strike out rate will be a benefit if he can sustain it because those are fewer outs that are left to chance. However, the increased walk and home run rates will quickly offset this. His ground ball to fly ball ratio hasn’t changed significantly (1.7 last year, 1.6 this year) so I doubt he is pitching that differently. Based on what we know so far, it’s too early to worry about Cornejo. But, I will be keeping an eye on these rate stats.

1 Comment

  1. Run Rate

    October 11, 2007 at 10:49 pm

    Glad to see someone is staying on top of things.