Having recently reported on how the prospective righthanded starters performed versus their 2012 minor league peers, I will now give the system’s lefthanded starting candidates their week under the microscope.
Lefthanded pitchers currently in the Astros organization who pitched mostly as starters during the 2012 minor league campaign and faced at least 150 batters at the High Rookie League level or above. Also included were the 2011 campaigns of two hurlers who fell shy of facing that many batters in 2012 due to injury.
These four stats were computed for each pitcher for each league they appeared in:
1. BB&HBP%. This is the sum of walks and hit batsmen divided by batters faced.
2. K%. This is strikeouts divided by batters faced.
3. LD&OFFB%. This is the sum of line drives and outfield flyballs surrendered divided by the number of non-bunted batted balls (100% minus groundball and infield fly ball rate).
4. OFLD&OFFB Pull Rate. This is the percentage of outfield line drives and outfield fly balls versus the pitcher that were hit to the batter’s pull-field third. As was the case for righthanded starters, minor league hitters’ batting averages (AVG) and slugging percentages (SLG) are similarly elevated when they hit a flyball or line drive to the pull-field third of the outfield against a lefty starter (.671 AVG, 1.390 SLG) versus when they hit a flyball or line drive to the center-field third (.430 AVG, .642 SLG) or opposite-field third (.398 AVG, .628 SLG) of the outfield.
Grading Each Pitcher’s Performance Relative to Their Peers
Each prospective organizational lefty starter was rated based on how many standard deviations better or worse they were versus their respective minor league level's average for a lefty starter at each of the first 3 stats; since the OFLD&OFFB Pull Rate stat cannot be easily tallied for all starters of a given minor league level, there I simply rated each pitcher versus a mean and standard deviation that were computed from a sample of 39 minor league seasons of lefthanded starters for which I have that data. Each ultimately receives a BB&HBP Score, K Score, LD&OFFB Score, and OFLD&OFFB Pull Rate Score using a scheme where a score of 50 indicates level average, any score above 50 is better than level average, and 10 points equates to one standard deviation. An Overall Score is also generated for each pitcher by giving their BB&HBP Score 20% weight, their K Score 36% weight, their OFLD&OFFB Score 22% weight, and their OFLD&OFFB Pull Rate Score 22% weight; the Overall Score gets scaled away from 50 such that 10 points again amounts to one standard deviation. To ease with comparisons, the five Scores are rounded to the nearest number ending with a zero or five. Note that being one standard deviation better than average is very good (a 60 score is comparable to equaling or bettering 84% of peers) and that being 2 standard deviations better than average is exceptional (a 70 score is comparable to equaling or bettering 98% of peers).
Keuchel rated very well at control and avoiding line drives and flyballs but struggled to miss bats and prevent hitters who did manage to loft the ball from pulling him; those extremes earned him an average Overall Score for a AAA lefty starter. Owens also rated as an average AAA starter overall but achieved that outcome by being near-average at each of the four stats. Oberholtzer rated well overall even with his line drive and flyball score and his pull rate score each dropping by almost a full standard deviation in AAA versus AA. Musick rated a bit below average during his injury-shortened 2012 season that was spread across 3 levels, mostly due to subpar batted ball stats. Walters was pulled quite frequently on line drives and fly balls, rating 2 standard deviations below average at the stat. Cain's weakness was at the strikeout. Rollins had the best Overall Score among the 4 listed lefty starters who were acquired via trade during 2012 and was particularly good at the punchout. Cruz quietly posted strong numbers in his third South Atlantic League season, though he did check in right on the league’s average age for a lefthanded starter. Bircher's undoing was his relatively high line drive and flyball rate. Holmes was particularly good at the strikeout and did surprisingly well at the pull rate stat given his sub-90 mph fastball average velocity; his 65 Overall Score earns top honors among the system’s 2012 southpaw starters. Hallock and Lee showed promise in their 2011 debuts only to see their 2012 seasons curtailed by injury.
Wrap-Up Graphs: Individual Scores of Lefthanded and Righthanded Starters
To graphically summarize the findings of the two statistical reviews, I will now pool the (non-rounded-off) scores of the lefthanded and righthanded starters and sort them from best (top) to worst (bottom). Recall that each pitcher’s score on a graph was determined by comparing their stat to those of starters of the same dexterity and minor league level(s) and that 10 points equates to one standard deviation (SD).
Please do comment away as to which of these Overall Scores you find most surprising in the positive or negative direction.