Jake Arrieta Optioned to AAA: Not (Entirely) His Fault

by Nate Delong
Delong writes about the Orioles over at Orioles Proving Ground. He is part of 2013's Expanded Roster, a feature where we provide local writers opportunities to expand their reach.  Click here to find all of Camden Depot's Expanded Roster entries for 2012.  2011 Expanded Roster items can be found here.  As always, feel free to provide the Depot with suggestions for posts or with your own interest in writing an items or several to be posted here. 

On Monday, the Orioles optioned Jake Arrieta, one of their talented but frustrating young pitchers to the minor leagues, due to his inability to consistently throw strikes.  With a career best 7.1% walk rate in 2012 (following walk rates over 10% in both 2010 and 2011), he’s never been known to have great command.  However, despite an improvement last year, he’s taken a quick step back in 2013, as his walk rate has ballooned to 18.4%.  To emphasize that point, he’s walked more batters (16) than he has given up hits (15), in 19 innings. Among starters with at least 10 innings pitched, Arrieta leads the league in BB% by more than 3%.  It’s easy to see that all of these walks are the primary culprit of his 6.63 ERA, despite his high strikeout rate and a BABIP (.292) in line with his career mark.

Arrieta’s lack of command has not only hurt the Orioles by putting extra runners on base, but it has also contributed to increased use of the bullpen, due to his high pitch counts.  The Orioles bullpen has pitched 61.2 innings (as of April 22), 12^th most in all of baseball.  Arrieta has contributed greatly towards the bullpen usage, as his 19 innings have come in 4 starts.  In fact, he’s averaging almost 20 pitches per inning, which limits his ability to pitch deep into games, even when he’s throwing relatively well.  For example, on April 16^th against Tampa Bay, he only allowed 1 earned run in 5 innings (despite walking 5), but he needed 112 pitches to do it, forcing the bullpen into action much sooner than normally needed in that situation.

      So why has Arrieta struggled so much more with his command in 2013 compared to previous years? 

      According to Pitch F/X data, Arrieta is actually throwing a career high percentage of pitches in the strike zone (51% versus 48.9% career rate).  However, despite that, opposing hitters are swinging less against Arrieta’s offerings this year by roughly 2.5%.  While that may not seem significant, it becomes more interesting when you isolate which pitches opposing hitters are laying off.  Take a look at the table below.  Compared to his career numbers, batters are swinging far less on pitches outside of the strike zone, specifically with respect to his 4-seam fastball, sinker, and slider (pitches Arrieta throws about 76% of the time).  

      There are two reasons why hitters may be swinging less at Arrieta’s pitches: 

1. Knowing that he doesn’t have great command, batters have changed their approach against him and are actively deciding not to swing as frequently; and  
2.  Arrieta is missing the strike zone by such a wide margin, that opposing batters aren’t even tempted to swing

I suspect that the answer is a little bit of both.  Below is a figure showing the location of Arrieta’s pitches where the opposing hitter did not swing. The figure also notes whether that pitch was called a ball or a strike.  As you can see, there are quite a few pitches that missed by a wide margin.  However, a closer look reveals that Arrietta may have been a little unlucky as well, as the majority of his borderline pitches (and even a significant number of pitches that appear to be inside the strike zone) were called balls.

While optioning Arrieta to the minor leagues is not ideal, I do not believe it’s a big issue moving forward.  There are reasons for optimism, namely his high strikeout rate (23%) and his continued success in limiting home runs (5.9% HR/FB ratio).  As with all stats this early in the season, it is extremely important to remember that his 19 innings in 2013 are a very small sample.  However that small sample works both ways, and if a couple more of those borderline pitches would have been called strikes rather than balls, his walk rate and ERA could look very different.  Arrieta is a talented pitcher with the potential to be a very productive member of the Orioles rotation if he can limit his walks.  Hopefully his time in AAA will be productive and brief, and he returns in a matter of weeks with increased confidence and command.