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Correlating Single-A walk and strikeout rates to the Major Leagues

How does a prospect's minor league walk or strikeout rate correlate to his rate in the majors?

Introduction

As I began my series of correlating prospect walk and strike ratios to future hitting success, a question arose from Carson Cistulli. How do minor and major league walk and strikeout rates compare to each other? I did a little of this analysis in my original series at The Platoon Advantage, but never pursued it in any depth. Consider this a supplement to the already running series.

Previous Levels: Rookie and Short-A

Method

I took the same data but instead split minor league seasons into various BB% or K% bins, basically the equivalent of Very Low, Low, Average, High, and Very High. Then I compared those rates with the player’s eventual MLB rate. If a player had fewer than 500 MLB PAs, I did not count his rate, since that is too small of a sample.

Hopefully the following tables are simple to understand, but just in case I didn’t design them well enough, I will explain. The first column contains the labels for BB% or K% at the minor league level. The third through eighth columns are the percentage of prospects that had that column heading’s major league BB% or K%. This means that rows add up to 100%, but columns do not.

Walk Percentage

The younger a prospect is, the better chance he has at making the majors even with a low walk rate. Only 17% of 19 year-olds with low walk rates end up with 0-499 MLB PAs, while 33% of 20 year-olds with low walk rates do. Very few players in the majors have 0-4% or 13+% walk rates for an extended period of time. Players at these extremes in the minors will generally regress or not make it.

Strikeout Percentage

High strikeout prospects don't tend to make it very far, even if they are younger. For the very young prospects, age 16-18, only those players with average rates have had an above average chance of sticking in the majors. Players over 18 follow a more traditional trend, where lower strikeout rates represent a high percentage of those who stick.

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Statistics courtesy of Fangraphs and Baseball Prospectus.

Chris St. John is a writer at Beyond The Box Score. You can follow him on Twitter at @stealofhome.