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— Where BTF's Members Investigate the Grand Old Game
Wednesday, November 02, 2005
Tweaking Zone Rating
Sean outlines a simple method for turning a player’s zone rating into runs prevented.
For most of baseball history, it simply was not possible to use statistics to evaluate defense with any accuracy. Much improvement has been made in the last 2 decades. Range factor, fielding runs, zone rating, win shares, and ultimate zone rating (UZR) are a few. From time to time a new system will come along and become the new standard, totally changing the ways we think about defense in baseball.
This is not such a system. I cannot hope to match something like UZR in accuracy. Instead, what I’ve done is combine data from several sources, all freely available, at least for this year. Zone rating is the base of the system. Also included are assists and errors for outfielders, and double plays for middle infielders. Catchers are rated on stolen bases, caught stealing, passed balls, errors, and wild pitches.
Compare the player to league average. Take plays made and subtract (plays available * position average zone rating). This tells you how many plays were made over an average fielder at the position, multiply by 0.75 to convert into runs.
This is done at the team level first. Here are the steps:
1. Estimate the number of runners the pitchers had on first base: (1B + BB + HBP – balks – SB – CS – PB – WP – pickoffs)
To apply to individual fielders, give half the credit to the second basemen and half to shortstops. The run value is 0.75 above a normal out. Double play runs are allocated to the second basemen and shortstops based on their percentage of innings played, though you could argue for allocating based on actual double plays turned instead.
1st and 3rd basemen as of now have no double play rating. I have no measure for a 1B ability to prevent errors.
Use putouts as a measure of plays made; otherwise the steps are the same as infielders for measuring plays save. I use 0.85 runs per play for the outfield, as more of the hits saved would be expected to go for extra bases.
Assist and errors: Get expected assists and errors by player inning total * league assist rate (or error rate) Compare actual to expected. Run value used is 1 for assists and 0.5 for errors
The statistics used are stolen bases allowed, caught stealing, errors, passed balls, and wild pitches. If you can find wild pitches by catcher, by all means use it. Otherwise, use team wild pitches and prorate based on the catcher’s innings played.
SB = - 0.19
The last measure compares stolen base attempts to the average stolen base attempts that an average catcher allows in the same number of innings. This gives some credit to catchers whose reputation keeps runners nailed to first (such as Yadier Molina) The run value represents the expected double plays from keeping the runner on first (0.1144 in 2005) times the run value of the double play (0.75)
C: JD Closser –11, Fasano, Kendall, Piazza –8
Some, such as the value of an outfield assist, are simply my best guess.
For all players with at least 250 innings at a position for 2005, you can download the results from this excel spreadsheet: 2005 Defense. For catchers, there is 2005 data only. For infielders and outfielders, I have included a true talent estimation, based on 4 years of data.
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