Here’s an email from Baseball Info Solutions:
After a considerable amount of study, we’re releasing the latest update to our Defensive Runs Saved (DRS) metric.
Since 2013, our video tracking has allowed us to chart the pre-pitch infielder positioning. That data allows for the evaluation of defensive performance for individual fielders on shift plays and allows us to break the DRS system into PARTs. PART stands for Positioning, Air Balls, Range, and Throwing.
With this new system, we can isolate each of the individual skills for a player and separate those from positioning, which is largely controlled by a player’s team.
One of the other biggest benefits in this new system is the inclusion of shift plays.
Given the dramatic increases in shift usage in recent seasons, thousands of plays each year had been previously excluded from individual player ratings due to the current system’s inability to separate the player and team’s positioning efforts from the player’s range and throwing contributions on the play. Since the new system accomplishes just that, there’s no longer any need to exclude these plays from individual player ratings.
How does this impact player value? The player who experienced the greatest increase in value in the new system was Athletics third baseman Matt Chapman, who went from 18 DRS to 34. This was a product of both crediting Chapman for his excellent fielding in defensive shifts and accounting for how the Athletics positioned Chapman. In the previous system, Chapman was being penalized for missing balls that he had no chance of reaching given where he was playing. In the PART system, Chapman’s positioning is taken out of his DRS and instead is assigned to the team.
Other players to receive DRS increases of 10 or more runs were Cardinals shortstop Paul DeJong, Rockies third baseman Nolan Arenado, Dodgers utility man Kiké Hernández (for his play at second base) and Cubs shortstop Javier Báez.
A comprehensive explanation of the methodology that produces the results will soon be available at FieldingBible.com and in the 2020 Bill James Handbook. They will be accessible at other publicly-available resources in the near-future as well.
When it comes to evaluating defense, we’re not yet quite all of the way there, but we’re getting closer. The introduction of the PART system provides a more accurate reflection of defensive performance.