Originally Posted by Homer Bailey
May be a bit of semantics here Puffy, as I think we're on the same page, but I don't think it's necessarily a flaw in how xFIP is calculated. It could be a flaw in how useful it is, but not calculated. xFIP just tells us what a pitchers FIP would be if he had a league average FB/HR rate. On a player by player basis you can assess how meaningful that actually is, but that's all the number really tells us.
I used the word "calculated" incorrectly.
It's calculation is what it is. You really can't calculate it incorrectly as long as you can add and subtract.
I meant how "xFIP is derived". If pitcher's HR/FB rates differ becuase of different skill sets (as opposed to luck), then there is (in my mind) a flaw in how xFIP is derived.