Over the last few weeks, I’ve converted the fielding stats available at The Hardball Times into a little plus/minus stat, similar to what others have done. Although Justin gives you a good, concise explanation on the methodology (and here’s his more detailed post on the subject, which I’d highly recommend), I wanted to try it myself and take you through an example. If you’re familiar with the process, which many of you may be, there’s probably nothing new in this post …
THT buys the data from Baseball Info Solutions, and they give you a few things to work with:
Balls in zone (BIZ) — This is the number of balls hit into a player’s zone over the course of the season. A player’s zone(s) is the area where fielders at that position convert at least 50% of balls into outs (more from Dave Studeman).
Plays — Number of balls converted into outs on balls in zone.
Revised zone rating (RZR) — This is simply: plays/BIZ. So if Khalil Greene has 300 balls hit into the shortstop zone and converts 250 of them into outs, his RZR is .833.
Out of zone plays (OOZ) — This is the number of outs a player makes on balls hit outside of his zone.
So, let’s runs through a little example of how to turn these four numbers into a plus/minus stat (all numbers are made up):
In zone:
Find the average RZR at each position (let’s use shortstop here): .850
Based on the avg. RZR at that position, find the number of plays a player should have, based on his BIZ: Khalil — 300 BIZ * .850= 255 plays made. Let’s say he actually has 265 plays made, so he’s plus 10 plays on balls in zone.
Out of zone:
Find average number of out of zone plays per BIZ at short: .135
Based on that number (.135), calculate the number of out of zone plays a fielder should have, based on his BIZ: Khalil — 300 BIZ * .135 = 40.5. Let’s say he actually has 40 plays, so he’s -1 play on out of zone balls.
Now add the two numbers together to get a total number of plays above/below average: Khalil: 10 – 1 = 9 plays above average. Since you generally want things measured in runs, rather than plays, convert to runs using Chris Dial’s plays to runs conversions. You may notice those numbers make a lot of sense, intuitively (at least to me): a play saved at short is worth ~.75 runs, while a play saved in center is worth ~.842 runs. Why? An out is an out, right? Well, hits that get by the shortstop are almost always singles and base runners usually gain only one or two bases. On the other hand, many hits into center are doubles or triples and base runners can more often take two or three bases.
Anyway, to finish it out, multiply plays above average by Dial’s number: Khalil: +9 plays*.753= +6.8 runs above average
That’s how I did it. Not too complicated, I don’t think — but please let me know if you have any questions or if I made any mistakes. What follows is some of the positives and negatives of this stat (in my opinion).
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Why I like this ’stat’
- It’s based on play by play data. Some fielding stats, like Range Factor or Baseball Prospectus’, aren’t based on play by play data. Baseball Prospectus uses a bunch of adjustments to try and estimate how many chances a player had. With THT/BIS’ data, you don’t have to do that, because it is based on play by play data. So you’ve got a pretty darn good idea of how many balls were in a player’s zone, or were “fieldable.”
- It’s based on performance both in and out of zone. I see a lot of people using RZR to measure fielding and while that’s great, I think you’re missing too much of the total picture (the OOZ balls) when you do that. So with some relatively easy calculations, you can turn it into a plus/minus stat, using both RZR and OOZ.
Limitations/concerns, etc.
- There are not many (any, really) adjustments, like you’ll see in something like UZR. Those adjustments may be for park, pitcher handedness, batted ball speed, and so on. Obviously, this stat isn’t on the level of a more detailed fielding metric like UZR or John Dewan’s plus/minus, but it’s free and I think it’s pretty darn good : )
- A ball is either determined to be “in zone” or “out of zone.” Take, for instance, a ball hit right at the shortstop. That ball may be converted into an out, say, 90% of the time. Now, take one hit on the fringe of the SS zone; maybe it’s converted into an out 55% of the time. Those balls appear to be equal, under this system (since they were both hit in the SS zone). Over the course of a year, you expect stuff like that to even out, and fielders to have a relatively balanced distribution of opportunities, but surely it doesn’t always (or, even, often) happen.
- There are no “opportunities” for out of zone plays. We know how many OOZ plays a fielder makes, but we don’t know exactly how many chances he had. I (like Justin and others) use in zone chances as a proxy to estimate OOZ chances, but this certainly may not be the best way to do it — maybe it is balls in play (or ground balls for infielders; fly balls for out fielders, etc.), maybe innings, I don’t know. Either way, it is an issue but I’m not sure of its significance.
- It is not an all-inclusive fielding stat. For outfielders it doesn’t include throwing arms, for infielders it doesn’t include double plays or line drives/pop ups, for first basemen it doesn’t include catching throws from other fielders, etc.
Hey Myron,
thanks for taking the time to explain this.
This is cool. And I also appreciate the limitations this have but it’s still better than just fielding percentages.
One question: the play has to end in an out, right? So, in the rare occassion where a SS made a nice stop for a ball hard hit up the middle that ended up as a single but stop a runner at second base from scoring, is that counted as a good play or just disappeared? I’m guessing it doesn’t count as a defensive play and it probably rarely occur anyhow. OK, just a thought.
Thanks, man.
Yeah, I think it’s *a lot* better than fielding percentage, range factor, etc.
On the play where a shortstop gets to a ball up the middle like that, I’m pretty sure he wouldn’t get credit for anything, although, as you note, he’s actually saving a base (but he wouldn’t get “penalized” either, because it’d likely be out of his zone).
Why don’t you just use Zone Rating if you’re going to include plays made OOZ?
Sorry, Richard — comment got held in the spam thing for some reason.
I don’t like regular zone rating because of the way it handles out of zone plays. The formula, as you probably know, is ZR= PO/(BIZ+BOZ)
Let’s take two examples:
Khalil has 400 balls hit into his zone … in one scenario, he makes 340 of those plays and adds 10 plays OOZ. That’s a ZR of .854 (350/410).
In another scenario, he makes 330 of 400 in zone plays, but adds 20 OOZ plays. That’s a ZR of .833 (350/420), despite the fact that he also made 350 plays.
J.C. Bradbury goes through a lot of it here: http://www.sabernomics.com/sabernomics/index.php/2004/07/thoughts-on-zone-rating/
The best ‘system’ (based on the freely available stats) is probably some combination between different metrics (which also use different sources, STATS and BIS).
MB, this all looks good. It does get kind of confusing with some of the positions not fitting the model as well as others. My question is, does this system take into account arm strength for outfielders? My guess is that it does not. Juan Pierre rated very high in this system for CF and he was moved out of CF this year due to his lack of arm strength. It seems that arm strength would be included for infielders as the infielders with good arms would complete more plays (especially on the bang bang close plays at 1st). What are your thoughts?
vr, Xeifrank
haha, I should’ve took the time to read the very last bullet before posting. Let me say that I enjoyed reading your post, as you did a good job of explaining it for both the novice and experienced stat fans.
vr, Xeifrank
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It is not an all-inclusive fielding stat. For outfielders it doesn’t include throwing arms, for infielders it doesn’t include double plays or line drives/pop ups, for first basemen it doesn’t include catching throws from other fielders, etc.
Glad you found it : ) I actually edited the post to add that part, so if you were reading via a feed or something, it might not have been updated.
Anyway, regarding your comment on infielders’ arms, I think you’re right — infielder arm strength is captured in the stat, for the most part. But it’s nice to see it broken down, too (check Pizza Cutter’s work for that) i.e., is Tulo good because of arm strength, range, hands, etc. (fwiw, my guess is arm mostly!) … you’re not really going to get that here.
Ah, good points. I didn’t think about the different divisor.
MB, what are the average number of plays (ie – .850/.135 for SS??) “in zone” and “out of zone” for each position? I want to run some numbers on 2008 fielding data, but I’m not sure what to use. I looked at Justin’s site and he has some numbers, but they are based on the 2006 season. Thanks!
vr, Xei
Xeifrank, no, those aren’t the numbers. Within the next few nights, I’m going to update my spreadsheet — I’ll post the numbers either here or in a new post.
At short (which I have done already):
6663 BIZ
5542 plays (in zone)
.832 RZR
874 plays out of zone (.113 OOZ/BIZ)
Not should if that’s what you’re looking for or not …
The .832 and .113 numbers for 2008 stats (SS) is what I am looking for. I will also look forward to the numbers at the other positions. Thanks for the hard work. Yourself and Justin are great assets to the baseball blogosphere.
vr, Xeifrank
Awesome. I *should* have those up tonight, along with team fielding ratings … if everything goes somewhat smoothly : )
And thanks for the compliment. If you need any help with what you’re doing, feel free to ask me or whatever …
The position data is in the new spreadsheet linked in my new post up top …