Hi AN. The more cosmopolitan of you may recognise me as one of the people who writes  for Lookout Landing, and the statistically inclined may be aware that I developed an advanced pitching statistic that's gaining traction across SBN (including the occaisional mention here) called tRA. I'm hoping that I can explain the motivation and methodology behind this stat to all comers in this diary*, and answer any questions folks here have about its use.

Please forgive the British English.

Motivation

As measures of pitcher skill wins, ERA, and WHIP don't cut it. The holy grail of pitching analysis is to determine pitcher skill independently of his team, and anything involving hits is not going to do that. A's fans are gifted with one of the top defenders in the game in the form of Mark Ellis, and I imagine that there won't be much argument from anyone that he makes your pitchers better with his glove.

Except there's a problem. A pitcher should posses the same ability whether he's pitching in front of the best defensive unit of all time or on a team of eight Jack Custs. The defence helps after the pitcher has done his thing. In order to get a handle on pitcher skill, we must somehow look at what happens before his teammates get involved.

Method

We can divorce the defence from our pitcher by looking at pure pitcher outcomes and batted ball profiles.

The former consist of strikeouts, walks, hit by pitch, and home runs. Barring some robbed homers and the possibility of Jose Canseco being involved, fielders have nothing to do with these outcomes. Batted balls mean the distribution of ground balls, line drives, fly balls, and infield popups. These are the plays that the defence can turn into outs.

I imagine that the vast majority of AN'ers are at least passably familiar with FIP, which is a statistic that weights the pure pitching outcomes against runs scored, and puts the result on an ERA scale. While an extremely useful stat and an upgrade on ERA, FIP fails to take into account the pitcher's ability to exert at least partial control over batted ball profiles.

tRA does. By determining the average runs scored and outs made on each of the defence-independent outcomes in each season and league, we can credit a pitcher with runs and innings pitched simply by looking at statistics that they have control over. The following statistics are accounted for in the tRA model:

Strikeouts (K)
Walks (BB)
Hit By Pitch (HB)
Ground Balls (GB)
Bunts (BU)
Line Drives (LD)
Outfield Flies (OFB)
Infield Flies (IFB)
Home Runs (HR)

The actual act of deriving the average outs/runs for each of these over the course of a season is fairly involved, so I won't go into detail here.

Once you know expected outs and expected runs, it's easy to calculate tRA:

xRuns/xOuts*27. There. Done. We now have a metric on the R/9 (NB: not ERA) that is completely defence independent. Is that enough? Not quite. Parks need to be taken into account. This is actually a relatively easy adjustment, made possible by a tonne of work from the folks at The Hardball Times. So now we've derived a park neutral, defence neutral pitching statistic. Hooray.

I hope that was easy enough to follow. If you have any questions, I'd love to hear from you.

*It's not a fanpost dammit.