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.
For the infield:
Start with zone rating, which can be found for all players on ESPN’s site. You’ll need to estimate how many plays were made and how many plays were available; this information is not there. For plays made, assists are a reasonable proxy for 2nd base, 3rd base, and shortstop. For 1st basemen, I use (assists/2 + putouts/6). Divide plays made by zone rating to get plays available.
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)
2. Get the number of groundouts. This total is available in the MLB.com stat section.
3. Estimate expected double plays = (league dp/league runners on 1b) * (groundouts/ average team groundouts)
4. Subtract expected double plays from actual double plays
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
CS = + 0.44
PB and WP (over or under league average) = + 0.28
Error (over or under league average) = + 0.48
SB attempts (over or under league average) = + 0.086
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: Yadier Molina + 12, Ivan “Bones” Rodriguez + 11, Mike Matheny +10, Joe Mauer +10
No surprises here
1B: Todd Helton +11, Darin Erstad +10, Mark Teixiera +9
On saving errors, I think Erstad saved a ton from Figgins and the other 3b, few from Kennedy, who rarely makes a bad play anyway. Orlando Cabrera was saved a few errors as well, but the official scorers are more responsible than Erstad.
2B: Mark Ellis +23, Mark Grudzielanek + 23, 3 tied at +15
3B: Scott Rolen +12 (only 56 games!), Eric Chavez +9, Freddy Sanchez +7
SS: Jack Wilson +28, Juan Uribe +15, Adam Everett +14
Great SS defense was on display in the world series. Uribe’s diving grab for the next to last out of the series: Was that play legal? Isn’t it foul if the player winds up in the stands? Still a great play.
LF: Cliff Floyd +16, Kelly Johnson +12, Carl Crawford +10
Every defensive system has at least one result that makes you say WHAT? Floyd is mine.
CF: Jeremy Reed +20, Vernon Wells +15, Aaron Rowand +14
RF: Alexis Rios +11, Jeff Francoeur +11, Austin Kearns +10
And the trailers:
C: JD Closser –11, Fasano, Kendall, Piazza –8
1B: Richie Sexson –15, Jason Giambi –12
2B: Bret Boone –18, Rickie Weeks –17, Alfonso Soriano –13
3B: Mark Teahen –21, Jorge Cantu –17, Hank Blalock –15, Alex Rodriguez –15
Cantu did this in part time, he was also –11 at 2B. In the field he’s Jorge Cannot.
SS: Michael Young –22, Russ Adams –18, Edgar Renteria –15
Jeter was near average at –3, that’s 2 years in a row.
LF: Manny Ramirez –25, Hideki Matsui –9, David Delucci –9
That figure includes a park factor for Manny, the only park factor used in these ratings. He’s at –32 without it.
CF: Ken Griffey –25, Jose Cruz –13, Mark Kotsay –11
Kotsay had some injuries, as for the others, I hate watching bad centerfielders who were drafted in the first round by the Mariners and whose daddies were good players in the 70’s.
RF: Jason Lane –15, Gary Sheffield –14, Matt Lawton –14
I wouldn’t have guessed Lane, he looked pretty good in the playoffs. Maybe its just because he dives all the time.
Many of the run values for game events come from Tango Tiger’s site, http://www.tangotiger.net/
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.
Posted: November 02, 2005 at 12:59 PM | 88 comment(s)
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