A look at DRC+’s guts (part 1 of N)

In trying to better understand what DRC+ changed with this iteration, I extracted the “implied” run values for each event by finding the best linear fit to DRAA over the last 5 seasons.  To avoid regression hell (and the nonsense where walks can be worth negative runs when pitchers draw them), I only used players with 400+ PA.  To make sure this should actually produce reasonable values, I did the same for WRAA.

relative to average out 1b 2b 3b hr bb hbp k bip out
old DRAA 0.419 0.416 0.75 1.37 0.44 0.41 -0.08 0.03
new DRAA 0.48 0.57 0.56 1.36 0.44 0.49 -0.06 0.02
wRAA 0.70 1.00 1.27 1.53 0.54 0.60 0.01 0.00

Those are basically the accepted linear weights in the wRAA row, but DRAA seems to have some confusion around the doubles.  In the first iteration, doubles came out worth fewer runs than singles, and in the new iteration, triples come out worth fewer runs than doubles.  Pepsi might be ok, but that’s not.

If we force the 1b/2b/3b ratio to conform to the wRAA ratios and regress again (on 6 free variables instead of 8), then we get something else interesting.

relative to average PA 1b 2b 3b hr bb hbp k bip out
old DRAA 0.22 0.38 0.52 1.16 0.28 0.24 -0.24 -0.13
new DRAA 0.26 0.45 0.62 1.17 0.26 0.30 -0.24 -0.15
wRAA 0.44 0.74 1.01 1.27 0.27 0.33 -0.26 -0.27

Old DRAA was made up of about 90% of TTO runs and 50% of BIP runs, and that changed to about 90% of TTO runs and 60% of BIP runs in the new iteration.  So it’s like the component wOBA breakdown Tango was doing recently, except regressing the TTO component 10% and the BIP part 40% (down from 50%).

I also noticed that there was something strange about the total DRAA itself.  In theory, the aggregate runs above average should be 0 each year, but the new version of DRAA managed to uncenter itself by a couple of percent (that’s about -2% of total runs scored each season)

year old DRAA new DRAA
2010 210.8 -559.1
2011 127.9 -550
2012 226.8 -735.9
2013 190.4 -447.5
2014 33.7 -659.9
2015 60.1 -89.1
2016 63.3 -401.2
2017 -37.8 -318.3
2018 -50.2 -240.4

Breaking that down into full-time players (400+ PA), part-time position players (<400 PA), and pitchers, we get

2010-18 runs old DRAA new DRAA WRAA
Full-time 13912 11223 15296
part-time -6033 -7850 -9202
pitchers -7054 -7369 -6730
total 825 -3996 -636

I don’t know why it decided players suddenly deserved 4800 fewer runs, but here we are, and it took 520 offensive BWARP (10% of their total) away from the batters in this iteration too, so it didn’t recalibrate at that step either.  This isn’t an intentional change in replacement level or anything like that. It’s just the machine going haywire again without sufficient internal or external quality control.

 


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