Wednesday, June 19, 2013

All Heat, Not Enough Change

In 2012, Kelvin Herrera established himself as one of the more dominant reliever in Major League Baseball. In 84.1 innings pitched he struck out 77 hitters and unintentionally walked just 21. On top of this, he ground ball percentage was an excellent 55.5% and opposing hitters hit just .250/.301/.342.

It was an excellent season and among the hesitations of Royals fans for 2013, a potential Kelvin Herrera collapse ranked low on the list. Unfortunately, that is what has happened and given the high leverage situations in which the Dominican reliever is utilized the issues are amplified. In 2013, Herrera has a 5.04 ERA. His walk rate has nearly doubled and while his strikeout rate has climbed to over a batter an inning, his home run rate has jumped from 0.43 per 9 innings to 2.88 per 9 innings.

What the hell is going on?

After Herrera's initial struggles in Atlanta, we were told that Herrera feared that he was tipping his pitches. Given the uniqueness of this series compared with the rest of his career, I couldn't help but wonder if there might have been some truth to that. However, when the struggles continued I began to notice Herrera's increased reliance on his fastball.

Now make no mistake about it, Herrera has a dynamite fastball. As a 5"11", 190 pound man it is incredible that he can consistently hit triple digits. However, these are big league hitters. If they couldn't catch up with fastballs, they wouldn't be playing at the highest level in the world. Relievers can find success with two pitches, but unless your name is Mariano* it is hard to do so with one.

The thing is that Herrera has another fantastic pitch. The gentlemen at Fangraphs even took the time to create this post as an homage to the awesomeness of the Herrera's change. Take a moment to watch these GIFs, it is worth your time.

I took a moment to test my hypothesis that in Herrera's worst outings he has been far too reliant on the fastball. Here is what I've found:

  • In 9 of 26 outings this season Herrera's FIP has been over 5.00 
  • In 14 of the 26 outings Herrera has thrown change ups less than 20% of the time. (In 2012, he threw change ups in 28.7% of his pitches). Seven of these resulted in FIPs over 5.00
  • In 12 of the 26 outings Herrera has thrown less than 15% change ups. Six of these resulted in FIPs over 5.00
  • In 9 of the outings he has thrown change ups 10% of the time or less. Five of these resulted in FIPs over 5.00
According my five second correalation analysis about 12% of the variance in FIP is accounted for by a decreased use of Herrera's change up. This isn't nearly as high of a number as I anticipated. Not that we believed this to be the case, but it appears that Herrera's troubles weren't totally the result of his pitch selection.

However, looking over the data we do find a trend in which Herrera is using his change up less and less. Perhaps he feels as though his change up is to blame for the meltdown earlier in the year and to compensate he is trying to simply blow it by guys. This is just a theory, but I think very plausible considering his youth and the explosiveness of the pitch.

Taking a slightly different look at the numbers we see that when Herrera throws less than 20% change ups (has happened 14 times) he has posted a FIP over 5.00 seven times, meaning 50% of the time he doesn't mix in change ups he gets lit up like a pumpkin. 

When Herrera mixes in his change up and throws it over 20% of the time, he has only had 2 outings out of 12 in which his FIP has been over 5.00. Basically, when he mixes in his change up, the odds are just one in six (16%) that he gets hit hard. This may seem like a lot, but last season this happened to Herrera in 10 of his 76 outings (13%).

This data tells me that the distinction that should be made is that not throwing a fair share of change ups will not necessarily lead to a bad outing..However, his bad outings are much rarer when change ups are mixed in on average once every five pitches. Basically, if Herrera and Perez can use his best pitch in the same way they did last season, Herrera's numbers would likely see a nice boost. 

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