A Question on Context-Adjusted Defense

by Anticon23 on Oct 15, 2009 1:43 AM EDT Comment 8 comments

Because I'm bored and because I love tinkering around with old systems, I thought I'd try and recreate Charlie Saeger's "Context-Adjusted Defense." It's a system that really isn't necessary because we have PBP systems, obviously, but I thought it'd be fun to try it out and maybe even compare it toUZR/PMR/Plus-Minus, etc.

Unfortunately, I've already hit a wall. Does anyone understand how to apply Saeger's "position rates"?

(((AB.rhb - HR.rhb - SO.rhb) * posRate) / (AB.tm - HR.tm - SO.tm)) / lgAVG

What the heck is the posRate? It is the "position rate," a measure of how much more likely a right-handed batter is to hit a ball to that position. Each affected position has a different rate:

1b

0.25

2b

0.50

3b

4.00

ss

2.00

lf

0.70

rf

1.30

A right-handed batter is four times as likely to hit a ball to the third baseman than a left-handed batter, and twice as likely to hit a ball to the shortstop than a left-handed batter. This sounds like a big difference, and it is, but teams don't vary much on the number of right-handed batters they face.

I don't know how to reach Mr. Saeger, and the only other person I've seen use them, DSG, hasn't gotten back to me on it yet. Chances are this is really simple and I'm overlooking something terribly obvious, but I figure it'd be worth a shot to see if someone here can enlighten me!

Thanks in advance.

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From the equation, seems like you're just multiplying the rates

The thing to which the position rate adjustment is multiplied is the number of balls in play hit when a position player was in the field. Since righties hit balls to shortstops twice as often as lefites, the adjustment to the balls in play are made such that the overall weights are 1 (so that you don’t have extra balls in play at a team level). Can anyone confirm this?

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by SFiercex4 on Oct 15, 2009 9:58 AM EDT reply actions 0 recs

DSG sent me an explanation. Once (or should I say if) I get it working right I’ll walk through an example.

by Anticon23 on Oct 15, 2009 7:13 PM EDT reply actions 0 recs

Position Rates

as DSG explained it. Not sure if I’ve got it right or not.

Let’s say you’re trying to figure out how many assists a third baseman should have made. Let’s say that on average, a third baseman makes .1 A/BIP, and the average team sees a 60/40 split of RHB/LHB (these numbers for illustration only, by the way). Using the position rate for third base (4), we can solve for the number of A/BIP we would expect a third baseman to make with a RHB at the plate versus a left handed batter:

.1 = .6*RHBrate + .4*LHBrate
RHBrate = 4*LHBrate
.1 = .6*4*LHBrate + .4*LHBrate
.1 = 2.8*LHBrate
LHBrate = .1/2.8 = .0357
RHBrate = 4*LHBrate = .142857

Then multiply the percentage of RHB and LHB a team faced by those rates and you’re done.

I applied it to the Rays’ 3B, and they were 45 assists above average. Longoria played 92% of Tampa Bays’ innings, meaning that he was somewhere around +41 plays. Converted to runs he’s somewhere around +9.9 runs saved by virtue of his range. Or something like that.

Then again, I’m not sure if I’m doing this right or not. I get the feeling that I’m not.

by Anticon23 on Oct 23, 2009 5:27 PM EDT up reply actions 0 recs

Yes

I think you have it correctly.

KJOK

by KJOK on Oct 23, 2009 5:47 PM EDT up reply actions 0 recs

Great

I tried to figure out context-adjusted fielding a few years ago, and couldn’t quite put all the pieces together given what was publicly available, so I’m very interested in what you find!

KJOK

by KJOK on Oct 22, 2009 1:49 AM EDT reply actions 0 recs

I can only get so far before I get overwhelmed. I honestly don’t think I have the time or energy to figure it all out, at least right now. Hopefully he has another article up somewhere else where he talks about his methodology, but this is the only one that I’m aware of.

by Anticon23 on Oct 23, 2009 5:33 PM EDT up reply actions 0 recs

Context Adjusted Links

There’s this:

http://www.baseballthinkfactory.org/files/primate_studies/discussion/emeigh_2002-11-13_0/

and this:

http://www.baseballthinkfactory.org/files/primate_studies/discussion/charlie_saeger_2002-09-21_0/

KJOK

by KJOK on Oct 23, 2009 5:48 PM EDT up reply actions 0 recs

Thanks

I hadn’t seen the first link; the second is the one I’ve been attempting to recreate. Sadly, I seem to have hit a wall. I’ll give it another go (hopefully) soon and see if I can get anywhere.

by Anticon23 on Oct 23, 2009 8:53 PM EDT up reply actions 0 recs