THE BOOK--Playing The Percentages In Baseball

Friday, September 29, 2006

Why Does Runs Created Make Sense?

Boring and with math gyrations that I typically don’t like, here’s how I see it:

Here’s the RC equation that I like to use:
Runs = .87 * PA * OBP * SLG

The .87 * PA term is better than AB, because this addresses the weakness in the RC with respect to walks. 

And, we all know that true run scoring is:
Runs = Baserunners * ScoreRate + HR

Presuming that 92% of the OBP rate is baserunners, we can rewrite this equation as:
Runs = (.92 * OBP * PA) * ScoreRate + HR

The scoreRate is about 40% of (SLG+OBP), more or less.  Not an exact equation of course, but will do the job for our purposes.  So:

Runs = (.92 * OBP * PA) * .40 * (SLG + OBP) + HR

Which gives us:

Runs = (.368* PA * OBP * (SLG + OBP)) + HR

Compare this to Runs Created:
Runs = .87 * PA * OBP * SLG

So, we see that the main portion, the PA * OBP * something on both sides.  Runs Created says it should be SLG, while in reality the HR portion should be stripped somewhat from that term.  The basic essence of RC makes sense, that you want OBP multiplied by SLG somewhat.

My illustration here makes most sense if the balance of OBP and SLG is what historically happens.