Here is how it works: The difficulty of turning a ball in play into an out is determine by several parameters: location of ball, how hard the ball is hit (soft, medium, hard), type of ball hit (e.g. ground ball, fly ball, line drive), handedness of batter and pitcher and ballpark. The expectation that a particular ball in play is turned into an out is determined by aggregation of this data for all games played in 2006.
Pinto then determined, for each fielder, how may balls were in play when he was on the field, how many he should have been expected to turn into outs and how many he actually turned into outs. The idea is that good fielders will record more outs than expected and poor fielders will record fewer outs than expected. David Pinto, himself, explains the whole PMR system in more detail on YouTube.
For example, 3808 balls were in play when Carlos Guillen was on the field. Based on all the parameters and data for all fielders, it was determined that Guillen should have turned approximatelly 455 balls into outs. In actuality, he turned 465 balls into outs. So he made 10 more plays than would be expected by the typical shortstop.
The other stats you'll see on Table 1 below are DER or Defensive Efficiency Ratio which is the proportion of balls in play turned into outs (465/3808 = .122), predicted or expected DER (455.45/3808) and the difference between actual and expected DER (.00251 in this example). The players are ranked on the difference.
Among 30 Major League shortstops with 2,000 or more balls in play in 2006, Guillen ranked 12th. Your first reaction might be: "but he made so many throwing errors so that negates his range". However, PMR takes care of that because he does not get credit for making a play if he throws the ball away. Instead, he gets penalized as he should.
The best shortstops according to PMR were Adam Everett (who made 35 more plays than expected), Billy Hall (+28) and Yuniesky Betancourt (+27). Two interesting names near the bottom of the list were Derek Jeter (who made 14 fewer plays than expected) and Miguel Tejada (-12). This will anger Jeter fans no doubt but it's not the first time he has found himself near the bottom of a statistical fielding list.
Table 1: PMR for Shortstops in 2006
|Player||In Play||Actual Outs||Predicted Outs||DER||Predicted DER||Difference|
|Jason A Bartlett||2570||348||333.97||0.135||0.130||0.00546|
|Ben T Zobrist||1395||173||165.55||0.124||0.119||0.00534|
|Aaron W Hill||1273||140||152.71||0.110||0.120||-0.00999|