In this recent FanPost, I showed how nearly every Astros minor league starting-biased pitcher performed in 2013 relative to their league peers using a novel fielding- and ballpark-independent outcomes statistical evaluation system. Having done that, I can average out the results of individual pitchers based on batters faced totals and quantify how those pitchers performed collectively as a group relative to minor league starters in general. Likewise, I can do the same for the starting-biased minor league pitchers of the 29 other major league organizations and ultimately compare the Astros' farmhands to theirs.
A Brief Reminder as to How Performance is Graded
The evaluation system charges each minor league pitcher with the number of runs shown in the table below for each such event they allowed in each league (bunts, foulouts, and plate appearances with a pitcher batting are ignored). Summing that over all 12 event types and dividing the result by the number of batters faced yields a single number of runs per plate appearance that quantifies how well the pitcher should have performed in 2013 in that league. Each pitcher then gets graded versus a core group of starting-biased pitchers in that league who met some minimum batters faced criteria. At that point the pitchers of a league can be ranked from best to worst on performance and they receive a Performance Score that expresses how well they fared. Note that whether an individual pitcher gave up a hit, home run, or allowed runs on a plate appearance is being completely ignored in grading their performance.
I also break the performance of each pitcher down into three sub-categories to better appreciate their relative strengths and weaknesses: Control Subscore, Strikeout Subscore, and Batted Ball Subscore. Those 3 elements explain 23%, 43%, and 34% of a pitcher's Performance Score, respectively, in a typical league. An Age Score is computed to quantify how young the pitcher was relative to league starting-biased pitchers; this is used purely as a frame of reference when interpreting a pitcher's results.
Only results accumulated above the two domestic lower rookie-level leagues (Arizona League, Gulf Coast League) are processed. The scores and subscores of all such Astros' minor league pitchers who averaged 10 batters faced per game are pooled and weighted based on batters faced totals to arrive at a single Performance Score, Control Subscore, Strikeout Subscore, Batted Ball Subscore, and Age Score for Astros' 2013 minor league starting pitchers. Each result will be expressed as a percentile here, where the percentile is the percentage of minor league starters who they bettered or equal on the parameter.
After repeating the process above for each MLB organization, we can rank the results to see how well Astros' minor league starters stack up versus those of the others.
Astros' minor league starters placed a comfortable first on overall performance and no worse than 6th on the associated subscores and Age Score. They placed 2nd on batted balls, 3rd on control, and 6th on both strikeouts and youth relative to level. Rating so well at strikeouts and batted balls is particularly impressive, in so much as those outcomes tend to be inversely related (Pittsburgh has a groundball-emphasis with their minor league pitchers, and the table shows how their 1st place finish in batted balls is offset by a correspondingly poor showing in strikeouts). The Astros rated particularly well relative to their divisional rivals (color-coded in the table).
With the tandem starting rotation system in place at essentially all levels for most of the season, the majority of the Astros pitchers encompassed in the table pitched every 5th day as the alternating front/back end of a tandem. Conversely, most of the other organization's starters pitched every 6th or 7th day in a traditional starting role. And we see that noteworthy difference play out in the batters faced column at the far right with the Astros' arms facing the fewest batters per game of the 30 organizations, and by a good margin of more than one batter per game less than the next lowest value. That makes it somewhat difficult to gauge just how much of the Astros' strong organizational 2013 showing on minor league starting pitcher performance stems from talent acquisition and development, as the tandem rotation setup could be skewing the results in the positive direction to some extent. Nevertheless, the take-home message remains that Astros minor league starting pitchers performed exceptionally well in 2013 relative to minor league starters in general, despite being rather young by league and level standards.