A note on minor league ground ball rates

While I continue to pour through mounds of Gameday data from Minor League games, I thought I’d stop and share some numbers. I haven’t found a “story” that’s compelling enough to write about yet. Nor have I finished running through the numbers.

In a nutshell, I compared “year 1″ and “year 2″ performances for all pitchers who faced at least 200 batters in one league in 2007 or 2008 to the same pitcher in another league in 2008 or 2009. For example, Joe Schmoe if pitched in the Southern League in 2007 and the International League in 2008, he goes into the pool. There’s all sorts of problems with this approach, namely I’m not filtering pitchers who may have had substantial experience at a higher level during “year 1″, but it does give some idea of how guys progress.

A pitcher with a 50% ground ball rate in the Southern League (Double-A) would project to a 45% rate in the following season in the Pacific Coast League (Triple-A). A 40% rate projects to 37% and a 60% rate to 53% (y2 = y1*.7702 + .0656; r2=.4693). This ignores any information other statistics may provide in projecting ground ball rates. It does, however, let me split players into some cohorts (out- or under-performed) to carve out some case studies and start digging up those key individual differences that muddy the statistical waters. In this particular group, outliers included Max Scherzer, Esmerling Vasquez and Greg Miller, for whatever that’s worth.

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Comments

  1. Cory Schwartz said...

    Harry do you believe the erosion of the GB rate to be due to scoring bias (I hope not) or due to the (presumably) tougher competition at higher levels?

  2. Harry Pavlidis said...

    I think it is talent/maturity, for a variety of reasons. But I’m still asking the data such questions.

  3. Brian Cartwright said...

    Maybe not tougher competition, but a different profile of batters faced.

    At each rise in level, the babip on fly balls fall while it holds steady on ground balls. I presume this is because at each higher level, the average fly ball has a higher vertical angle – more homeruns, but easier to catch when it stays in the park. This could be the result of a promotion bias which favors homerun hitters.

  4. Brian Cartwright said...

    But how soon would they have hit f/x in the minors?

    As soon as I get a break from coding the forecasts, I would run these tests – compare GB% of batters who were promoted to those who weren’t. If I am correct, promoted batters would have lower GB%, but should remain relatively steady as they are promoted. Pitchers, on the other hand, I was expect to have decreasing GB% as hey are promoted.

  5. J. Cross said...

    Harry, do you see this same decrease in GB% across all movements to higher levels (a -> aa -> aaa -> mlb)?

    I’d definitely be interested in hearing more about how a pitcher’s GB% can be expected to change as he moves from the low minors up to the majors.

  6. Harry Pavlidis said...

    In short, similar trends. And you will see more. I’m working on that for Tuesday morning on the main site, including Brian’s question.

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