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October 22, 2003

Getting PADE, Redux

A Few Adjustments

by James Click

Last time, we cooked up a way to remove park effects when looking at Bill James' Defensive Efficiency, a stat that measures the percentage of balls in play fielded by a team's defense. The new metric, tentatively called PADE, ranked teams on a zero-centered scale, showing how well a team performed against the league average with their given schedule. The intent was to more fairly judge defenses against each other rather than punish teams like Colorado and Boston for having to play in more difficult venues.

As stated before, defense can be broken down into many facets, but the three most prevalent parts are park factors, pitching, and actual defensive performance. Since we've already figured out how to remove the first one--park factors--the next logical step is attempting to correct for pitching, leaving us closer to a metric that measures only defensive performance.

To do this, we'll take a similar approach to the first version of PADE, but instead of defensive park factors, we'll use defensive pitcher factors. The first step is to determine an expected defensive efficiency for every pitcher, based on their career history.

Looking for defensive efficiency ratings sorted by pitchers inherently concedes that pitchers have some degree of control over the number of hits per balls in play. This concession will not sit well with many readers, mostly owing to Voros McCracken's article of a few years ago. To sum up very quickly, McCracken broke down pitching into statistics over which the pitcher had control (BB, HBP, SO, HR) and those over which he does not (hits on balls in play--a stat he called IPAvg for "In Play AVG"); from there, he pointed out that pitchers have little if any control over the percentage of their balls in play that become hits. Since the publication of this article, there has been a great deal of research surrounding his conclusions, most notably by BP's Keith Woolner and Diamond Mind Baseball's Tom Tippett. Based on their research, McCracken has softened his original conclusion and it's now safe to say that pitchers do have some control over their IPAvg, especially when considering large sample sizes.

Back to what we were getting at: in order to attempt to remove the quality of pitching from our defensive metrics, we need to establish just how difficult it is to play defense behind each team's pitching staff. For a first attempt, we'll establish an expected IPAvg for all pitchers, simply averaging their total career numbers. Rather than look simply at the last three years as we do with park factors, it's important to look at a pitcher' s total career because of the large variation in IPAvg from year to year. Armed with an IPAvg for every pitcher, we simply weight that by how much of the pitching they did for their team and produce an expected defensive efficiency based on the pitching staff (PitchDE). Here are the results:

Team                    PitchDE
Seattle Mariners         .7286
Anaheim Angels           .7227
Tampa Bay Devil Rays     .7221
San Francisco Giants     .7182
Arizona Diamondbacks     .7171
Oakland Athletics        .7146
Chicago White Sox        .7140
Los Angeles Dodgers      .7132
Cleveland Indians        .7131
Baltimore Orioles        .7129
St Louis Cardinals       .7116
New York Yankees         .7108
Philadelphia Phillies    .7099
San Diego Padres         .7096
Atlanta Braves           .7093
Boston Red Sox           .7091
Minnesota Twins          .7082
Chicago Cubs             .7077
Cincinnati Reds          .7072
Montreal Expos           .7068
New York Mets            .7061
Houston Astros           .7060
Kansas City Royals       .7059
Florida Marlins          .7053
Pittsburgh Pirates       .7053
Toronto Blue Jays        .7046
Colorado Rockies         .7041
Detroit Tigers           .7003
Milwaukee Brewers        .7000
Texas Rangers            .6964

Obviously there are some problems here. Primarily, there are quite a few rookie or relief pitchers with small sample size problems, making younger staffs more susceptible to outliers that skew the numbers. Next, there's the problem of pitchers having spent too much of their time in one park or in front of one defense. This is mainly a problem with teams laden with homegrown talent who pitch in extreme parks (see: Athletics, Oakland). Finally, there's the slight problem of pitchers who have been around long enough to have significant playing time in the late '80s and early '90s when the game was played slightly differently.