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— Where BTF's Members Investigate the Grand Old Game
Tuesday, March 06, 2001
A Defensive Stats Primer
Defense! Defense! Defense! Can’t tell the difference between a Zone Rating, a Range Factor, or a Max Factor? Hit the link to get clued in.
Baseball is made up of two things scoring runs, and preventing runs from scoring.? The pitcher is all about keeping runs from scoring and the Designated Hitter is all about scoring runs.? Any manager using a weak hitter at DH is clearly unfamiliar with the purpose of the role.? Every other player has two parts to his game ? his hitting and his fielding.
Offense has been studied thoroughly.? There are many ways to evaluate offense: batting average (BA), on-base average (OBA), slugging average (SLG), Runs Created (RC), Extrapolated Runs (xRun), Linear Weights (LC).? The last three offensive summations do a really good job of describing how runs are scored on a team level, and that is subsequently extended to the individual players.? All of these methods are readily available around the Web, with xRun?s progenitor being BB Primer?s own Jim Furtado.? You can read all about it in the glossary.? You can calculate the approximate value of every player, and essentially determine the league?s offensive MVP.
Defense is a bit trickier to measure.? Is it the pitcher getting the hitter to hit into easy plays, or is there a big difference in defensive players?? A quick glance at each team?s opponents? batting average will tell you there is a limited amount of contribution a single defensive player can make.? The important question is how much better is a defensive player than the available alternatives, and ultimately his peers.
The common defensive statistics, unlike offensive statistics, stink.? First there is ?Number of Gold Gloves Won.?? What do Gold Gloves say about a player?? As I read Dan Szymborski write the other day, ?he got the most votes.?? There is no objectivity to Gold Gloves whatsoever.? The voters usually vote for the player with a good reputation, regardless of actual skill level.? This really came to light in 1999 when Rafael Palmiero won the award after playing just 28 games at first base for Texas.? Sometimes a good fielder wins the award, sometimes not.? So using ?Gold Gloves won? is essentially useless for determining who is a good fielder and who is not.?
Next is fielding percentage (F%).? It?s nice to have a good fielding percentage, but it does little to tell you about how good a fielder is.? Two shortstops get 100 balls hit in their general direction.? Shortstop A fields 85 of them and makes no errors.? The other 15 are out of his range.? His fielding percentage is 1.000.? Shortstop B fields all 100.? He makes 5 errors (fielding or throwing).? His fielding percentage is 0.950. ?The difference between the two is not that SS A is better; in fact, he?s worse, but has a better percentage.? Pardon my blasphemy next: many of the ?great fielders? were really just limited in range.? Larry Bowa was a fine shortstop and has the highest fielding percentage for a career at short.? But Dave Concepcion was much better.? He just could range further, turning grounders into outs that Bowa was unable to reach.? Fielding percentage may be a good indicator of sure-handedness, but it doesn?t do a good job at all for determining who the better fielder is.?
In the ?80s, Bill James came up with a statistic called Range Factor (RF).? At first blush, this appears to be a good idea.? It is calculated by dividing plays made by games played.? This provides the number of outs a player made per game.? By comparing fielders to one another, one could quickly see that Ozzie Smith was making 5.5 plays per game and Garry Templeton was making 5.0 plays per game.? At 0.5 more plays a game for 160 games meant 80 singles!? Wow!? And that?s how a legend is born.? Bill James is known for giving rise to a new way to look at baseball: analytically, rather than just nodding along to the clich?s.? RF is not a statistic to use if anything else is available.? RF was modified to be calculated to plays per 9 innings.? What RF misses is the critical aspect of chances.? The reason Ozzie made 0.5 more plays per game is because he had more balls hit to him.? Ozzie had a lot more groundballs hit to him. That?s a big help.? The aspects of a fielder?s pitching staff influence this statistic more than most. Range Factor, because of its source and relative ?newness?, finds popularity in people just delving into the atypical statistics of baseball.? To me, that?s bad; very, very bad.? RF may have value over a career, but in today?s game, I think it is the worst.
So what do we do for a defensive statistic that doesn?t stink?? We start scoring baseball games for the fielders in addition to the hitters.? How?? We write down every ball that?s put into play, and where it was hit on the field.? There is a company that does this:? STATS, Inc.
STATS, Inc. is a company that hires people to watch baseball games.? These people write down every pitch.? They write down every play.? This is where we get information about how hitters perform with runners on second and two outs.? This is done to record what location every ball put in play was hit.? This is where we get information about how many times a pitcher throws to first base during each game.? Each ballpark has a grid with labeled ?zones?.? When a ball is put in play, the STATS scorer records the pre-labeled area of the field that the ball was hit to; how far the ball traveled before being picked up; whether it was a fly ball, a line drive or a ground ball, and an estimate of how hard the ball was hit.? The scorers do not make any judgment with respect to whether or not a fielder should have made the play.? This is critical because it removes the primary source of subjectivity in a player?s evaluation. ?STATS usually has several people watching every game.? Multiple game scores can be cross-checked to insure accurate ?zone? assignments for each ball in play.? It?s really a strong network of data collection, but it is not perfect.??
So you say, ?Dial, what does that have to do with the price of peas in Peoria??? And I answer: it?s how we can see how well a player does compared to his peers defensively.? The data accumulated by STATS is reported (at STATS on AOL, CNNSI.com, ESPN.com) as a zone rating.? Every player has one, and it is close to the fraction of balls a player converts into outs divided by balls hit into a player?s zone.? A player gets a bonus for getting to balls outside his zone.? For a good visual, consider the standard position for each player:? where the shortstop stands, where the second baseman and centerfielder stand.? For infielders, imagine a 20-foot circle around each player.? That?s the area each player is expected to cover.? All shortstops are responsible for the same zones.? Since they all are assigned the same zones, and they all stand within a few feet of each other on the field, the percentage of balls they turn into outs should be a mostly accurate description of how well they field.? Zone Rating (ZR) is not a perfect measurement, and should only be described as good.? It will undervalue defense because it doesn?t consider the ability to get to pop-ups and turn double plays.? If you need to make a judgement on how good a fielder is, try to use ZR at a minimum.
Unfortunately, there is no ZR data older than about 1985.? That means the Gold Gloves, the fielding percentages and range factors for all the older players will have to suffice.? There are a few systems attempting to measure fielding using play-by-play data, and they may improve on what we presently have, but one must always recognize the shortcomings of these systems and of the statistics gathered today.
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