What fielding metrics make up the SDI?
The SDI is built from two types of defensive metrics — those that come from batted ball location-based data, and those which originate from the play-by-play records of games. We gave more weight (70%) to the batted ball location-based metrics, which evaluate the degree to which a fielder makes plays in specific zones on the diamond. The player's performance is measured in comparison to his peers. The play-by-play based metrics (30% of the SDI) are important in that they approach defensive measurement from an alternative vantage point — a more generalized approach that estimates the number of batted balls hit into a fielder's area.
Within the batted ball location-based category, we've included 3 measures — Defensive Runs Saved (DRS) from John Dewan's company, Baseball Info Solutions; Ultimate Zone Rating (UZR), authored by noted sabermetrician Mitchel Lichtman; and Runs Effectively Defended (RED) from Chris Dial. The play-by-play based metrics include two measures: Defensive Regression Analysis (DRA) from Michael Humphreys and Total Zone Rating (TZ).
What are some of the defensive elements that are measured within the SDI's components?
Fielding metrics included in the SDI capture a fielder's range, his throwing arm, his sure-handedness, his ability to turn double-plays (for SS and 2B), his ability to convert bunts into outs (primarily P, C, 3B, and 1B), scoops of throws in the dirt (1B), as well as the number of "excellent" and "poor" fielding plays. In addition, for outfielders, his ability to prevent runners from taking an extra base is also rated. For catchers, blocking balls in the dirt and stolen bases/caught stealing are also included in their ratings. Finally, for pitchers, we include his ability to control the running game by holding runners on base, in addition to many of the above criteria. (Pitch framing by catchers is not currently included in the defensive metrics that comprise the SDI.)
