THE BOOK--Playing The Percentages In Baseball

I realize that you (Tango) were purposely not including “luck” in your list, but it is certainly a big part of RA/9 that is not included in xFIP.

Why choose such a circuitous route (RA/9-FIP) anyway?  Team BABIP, otherwise known as DER, gives you a decent idea as to team defense, although it obviously does not account for the type, locations, and speed (and other things) of batted balls or park effects.  If you want to do a little better, DER adjusted for the GB/BIP of the pitching staff is pretty good.  Or just go to FG and check out team UZR!

MGL, I think I got it covered in #3.

Otherwise, “luck” would apply to FIP and RA/9, if we mean the performance relative to the true talent. 

But, if we focus purely on an observation basis, there’s no need to talk about luck is there?

Tango, not really. If a pitcher’s FIP were 4.50 but he allowed 6 rpg, with a BABIP of .350, the difference between the FIP and the RA could possibly be:

1) His BABIP talent (e.g. that might be .305 rather than the league average of .300 or whatever it is).

2) Fielding (the fielders might be bad or HAVE performed badly when he pitched).

3) Park factors (the true BABIP in this park could be .305).

4) Situations (he might have allowed lots of hits with runners on base).

5) Luck (lots of bloops and bleeders).

All of these things are independent.  #4 (your #3) involves luck, but that is not the only way that luck can manifest itself.

Right, but FIP includes HR, which could have lots of “just enough” HR as well, or lots of 3-2 “lucky” strike 3 calls.

That’s what I meant when I said luck applies to FIP as well.  Indeed, luck applies to ALL observations, as we know.

That’s why I said that if we focus purely on the observation, then other than the binomial aspect of any observation, what else will account for the difference between FIP and RA/9.  That is GIVEN the outcome, what can account for the differences.

That said, I agree with you.

Don’t forget stuff like pickoffs and controlling the runner game.  I would think that for pitchers on the extreme ends of those (like Chris Young and Andy Pettite) those factors would contribute sizable difference.