RESEARCH: Revisiting expected HR/9

We know that about 10% of fly balls go for homeruns, ergo HR/9 is generally around 10% of FB/9. The Forecaster’s Toolbox tells us that homerun rate year to year can be expected to regress toward this rate. But how does this estimate do at predicting next year’s home-run rate?  

Voros McCracken’s DIPS was published in 1999 and DIPS 2.0 was published in 2002. Since then, there has been a lot of baseball played, and a wealth of batted ball data collected. Can we find a better prediction of next year’s home run rate?

The Basics

Let’s revisit the assumption about HR/FB.  Is it still true?  Below is data from 2002-2014 for pitchers with 80 IP or more, showing HR vs FB.

Homeruns per Flyball

Constraining the intercept to zero, we see HR = 0.102 * FB. The...


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