Ever since Voros McCracken published his original article on DIPS in 1999, sabermetricians have been attempting to isolate pitching from fielding. Tody the most widely used metrics are Tom Tango's FIP and Graham MacAree's tRA; FIP focuses solely on strikeouts, walks, and home runs allowed, while tRA also accounts for batted ball type. Yet possibly the best defense-independent value metric is little-known PZR, or Pitcher Zone Rating.
Skill vs. Value
Before I go any further it is necessary to distinguish between skill and value. Colin Wyers provides possibly the best overview of this issue:
People tend to lean upon defense-independent estimates of pitching performance because they better predict future performance. (And, strictly speaking, they do.) This leads to a lot of fantastic confusion about the issue, with the argument being that if we want to look at past performance, we should ignore defense-independent measures and look at actual results.
This is wrong for the same reason that we look at a pitcher's ERA instead of his win-loss record. A team does not consistently score the same amount of runs every game; thus it is possible for different pitchers, even different pitchers on the same team, to have vastly different amounts of run support. This is not a function of pitching, and the credit or blame for this should not righly be assigned to the pitcher.
It is the same with defensive support. Two pitchers, even two pitchers on the same team, cannot be presumed to have the same quality of support from their defense. Defense-independent pitching statistics seek to give us a way to compare pitchers with different defensive support fairly.
In other words: Given a league-average defense, what would the pitcher's statistics look like (and by extension, how many runs would he allow, and how many wins would he be worth)? Rather than trying to correct for all the "luck" in a pitcher's line, we are simply trying to isolate pitching from fielding.
The idea behind PZR (Pitcher's Zone Rating) is simple: for each batted ball, the pitcher is credited or debited with a fraction of a run, depending on the ball's location, trajectory, and speed. Essentially, PZR is UZR, but from a pitcher's perspective. As a result, PZR is a poor estimator of a pitcher's true talent level. It doesn't address the fact that pitchers have very little control over the location of a batted ball (apart from pulled, up the middle, or opposite field), nor does it regress line drive rate or HR/FB rate. But PZR is perfect for retrospective valuation. Like linear weights for batters, it evaluates players solely on what actually happened. Unlike FIP or tRA, it attempts to measure a pitcher's value at inducing "fieldable" balls in play. And it is truly "defense independent," as it replaces a pitcher's defense with a hypothetical league-average defense.
PZR is not a new idea. David Pinto came up with it in 2003, and it was discussed extensively at the Book Blog here and here. Also, MGL released PZR for pitchers from 2001-2006 here. However, PZR is not currently available in a daily-updated fashion the way FIP, xFIP and tRA are. The closest metric to PZR is Rally's WAR for pitchers. He uses the same methodology as PZR; however, his fielding statistic, TotalZone, is based on Retrosheet data rather than the BIS data that UZR uses. Furthermore, Rally only updates his WAR at the end of the year.
And so I come to the purpose of this fanpost. If possible, I would appreciate it if someone could post daily-updated PZR to a website. This would allow for the calculation of PZR-based Win Values, similar to the FIP-based Win Values on Fan Graphs. Another possibility is to use the HIt f/x data: if it's updated daily, I could calculate PZR based on HIT f/x parameters and gameday hit locations. This process would be similar to Peter Jensen's skill dependent batting runs, although I would incorporate hit location data and (maybe) an approximation of hang time.