Aaron Crow, Starting Pitcher: Maybe Not The Best Idea

Aaron Crow of the Kansas City Royals throws in the ninth inning during a game against the Chicago White Sox at Kauffman Stadium in Kansas City, Missouri. (Photo by Ed Zurga/Getty Images)

With Jonathan Broxton on board, Aaron Crow is getting an audition for the rotation. But should he?

The Royals weren't very good at many things in 2011, but there were two areas where they stood out: player development, and their bullpen. Those were partially linked, thanks to the performances of rookie relievers like Aaron Crow. While the ultimate fruits of their development labors are yet to be seen, Kansas City made one move to help keep the 2012 bullpen as good as the previous season's by signing Jonathan Broxton

The downside to this move, though, is that there are only so many innings available for relievers.(Even relievers coming in after Royals' starters.) Because of this, Crow is getting a chance to move into the rotation in 2012. In some ways he is an obvious fit: he posted an ERA of 2.76 last year, was drafted as a starting pitcher in the first-round not once, but twice, and has a nasty out pitch in his slider.

The presence of some positives doesn't mean it's a good idea, though. Crow moved to the bullpen in 2011 for a reason, as he struggled throughout 2010 as a 23-year-old in the minors. In his 163 frames, split between High- and Double-A, Crow posted an ERA of 5.73, striking out just 6.8 per nine in Double-A while showing control problems.

The Royals bumped him to the majors despite these issues, but placed him in the bullpen. He excelled, striking out 9.4 batters per nine and posting an ERA+ of 149. His walks were still a problem, but control isn't as much of an issue for relievers as for starters. Nate Silver wrote about this back in 2006, when it wasn't clear just yet whether Jonathan Papelbon's future was as a starter or reliever:

Walk rate--command--is strongly associated with the consistency of a pitcher's mechanics. Pitchers who have difficulty maintaining the same release point from inning to inning, or have trouble keeping their focus, are prone to bouts of wildness. Turning such a pitcher into a reliever can minimize this disadvantage, as he is less prone to fatigue, and may be able to get away with using just one or two pitches.    

Crow did this very thing, focusing almost entirely on his fastball and slider in 2011. He used his mid-90s heater 54 percent of the time, and his slider one-third of the time. That slider induced whiffs 26 percent of the time it was thrown -- nearly double the effectiveness of a league-average slider. Because he was able to focus more on his two best pitches, it didn't matter as much that he had a difficult time throwing strikes overall -- Crow threw every one of his pitches for strikes less often than your average hurler.

As a starter, he will need to expand his repertoire, utilizing his rarely-seen curveball in order to mix things up. It doesn't miss a ton of bats, and he has a difficult time throwing it for strikes; there is trouble in that pitch's future. 

Silver also discussed what you can expect from a pitcher moving from starting to relief:

...the typical pitcher will have an ERA about 25% higher when pitching in a starting role than when pitching in relief. That is, if you take a given reliever with a 3.00 ERA, your best guess, all else being equal, is that his ERA as a starter would be 3.75.

Does that mean that the average starting pitcher has an ERA 25% higher than the average relief pitcher? No, it does not. Over the past decade or so, ERAs of starting pitchers have run about only about 7% higher than relief pitcher ERAs.

Why the disconnect? The simple answer is that starters, as a group, are better pitchers than relievers. Starting pitchers, after all, are throwing the bulk of your innings.

Crow had a 2.76 ERA, so that 25 percent jump would put him at 3.45 as a starter. But that's not quite how it works, as in Silver's example, he is talking about your average climb in ERA. Things could be much worse, depending on the pitcher. Whether Crow was actually that good as a reliever is also up for debate, given his 4.11 FIP. Add 25 percent to that figure rather than his actual ERA, and Crow is expected to be somewhere over 5.00 as a starter. That's a huge (and ugly) difference, and it's not even fully taking into account what happens if his command and control don't improve, or his curveball fails to develop as needed.

Tom Tango's "Rule of 17" is another solid guide for these conversions: K/PA is up 17 percent as a reliever, BABIP is down 17 points, and home run rate is down 17 as well. Viewed through that lens, Crow's 2011 stats would be at about 7.8 strikeouts per nine, 1.4 homers per nine, and a BABIP of roughly .313. Since walk rate remains a problem -- and is expected to remain flat moving from relief to starting -- those homers would likely be for extra runs more often than not.

The Royals have nothing to lose here, as their rotation is terrible with or without Crow, but at first glance this seems like a temporary move given his pitches and problems. When Crow throws in the spring, be on the lookout for his curveball -- he's going to need it to work for this experiment to succeed in the long-term.

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