A Statistical Breakdown of the 2013 Midwest League's Pitchers Under 21, Featuring Julio Urias


In what follows, the performance of starting-biased pitchers who were 20 or younger during the entirety of the 2013 Midwest League season will be graded against that league's starters in general, using a fielding- and ballpark-independent statistical evaluation system.


What the Scores Mean

"Performance Score" amounts to the pitcher's overall grade for the Midwest League portion of their season relative to other league starters and is evaluated over every plate appearance that did not feature a foulout or bunted ball in play; it effectively assumes that the 2013 Midwest-League-average effect on run expectancy occurred in every instance of each of 12 possible plate appearance outcomes:

  • walk or hit-by-pitch (+0.32 runs)
  • strikeout (-0.28 runs)
  • infield flyball (-0.28 runs)
  • groundball to batter's pull-field (-0.08 runs), center-field (-0.01 runs), or opposite-field (-0.06 runs) third of the diamond
  • line drive to batter's pull-field (+0.39 runs), center-field (+0.36 runs), or opposite-field (+0.31 runs) third of the diamond
  • outfield flyball to batter's pull-field (+0.35 runs), center-field (-0.01 runs), or opposite-field (-0.03 runs) third of the diamond

Mathematically, a pitcher is charged that many runs for each such event, and ultimately that sum is divided by the total number of batters faced to arrive at a single runs per plate appearance value for each of them; those values then get ranked on a 20-to-80 scale and that number becomes their respective Performance Score.

The Performance Score can be broken down into 3 components to better assess the pitcher's relative strengths and weaknesses; these are their Control Subscore (references BB+HBP%), Strikeout Subscore (references K%), and Batted Ball Subscore (computed like Performance Score, but with the non-batted-ball events stricken from the numerator and denominator). An Age Score is tabulated independent of the performance measures and simply quantifies how young the pitcher was versus the league's average age for a starting pitcher in 2013. As for interpreting the scores and subscores, any 10 points equates to one standard deviation (SD) and:

  • a 70 amounts to 2 SD better than league-average (topped or equaled 97% of peers)
  • a 60 amounts to 1 SD better than league-average (topped or equaled 83% of peers)
  • a 50 amounts to league-average (topped or equaled 50% of peers)
  • a 40 amounts to 1 SD worse than league-average (topped or equaled 17% of peers)
  • a 30 amounts to 2 SD worse than league-average (topped or equaled 3% of peers)


Study Population

A total of 136 Midwest League pitchers met the two batters faced requirements (>200 total, >10 per game). Here we will look at how the 27 of them who were under 21 years of age for the entirety of the season (plus 2 bonus arms that did not quite reach 200 batters) fared relative to that sample of 136 pitchers.


The Scores

In the tables that follow, values that bettered the league average for that quantity by at least 1 SD are highlighted in green text ("very good") whereas those that trailed it by at least 1 SD are in red text ("very bad"). Asterisks indicate lefthanded throwers.

Though Urias barely qualified for the sample given his two lowish batters faced values, it remains rather remarkable that he was both the youngest of the 136 qualified pitchers and the best performer of them per this system. Elbow failure denied Osuna entry into the sample of 136, but the table shows that he would have scored quite similarly to his countryman if he had stayed healthy and performed as he had been going. Stephenson had the 2nd highest Performance Score of the 136 qualifiers, and that was fueled primarily by having the highest Strikeout Subscore (K%) of that group.


The South African Unsworth makes a surprise appearance placing third among the 136 qualifiers; his strong showing was the result of phenomenal control combined with an excellent batted ball profile and that would stand to make Unsworth not unworthy of your 2014 attention. Guerrieri, himself another elbow victim, and McCullers were the other twenty-or-unders who posted a Performance Score that bettered league-average by a SD; Guerrieri was a batted ball standout whereas McCullers was a strikeout standout. A few names in the rest of the table show up in at least some MLB Top 100 prospects lists, and while each of them were very young by league standards one would have to weigh how much their statistical performances should affect their rankings in such lists.


Batter Handedness Splits

Those scores and subscores can be recomputed looking only at lefthanded batters (LHB) or only at righthanded batters (RHB), and here are how the results look when that is done.


Note here that in some cases already smallish data samples are being cleaved still smaller. As with the earlier numbers, current performance relative to league starters is what is being measured - the objective isn't to predict the future of these prospects but rather to measure where they stand on a select set of measures at a single interval of time. And given that these hurlers are in the relative infancy of their professional careers, these values provide a series of baseline references against which to track prospective changes in performance while largely eliminating the effects of fielding and ballpark factors. Lastly, as always, scouting reports matter immensely and data like this should be viewed as a supplement to that information.


Ask the Audience

So which prospect's numbers do you find most surprising? Comment away below if the poll does not suffice.


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