Both Fangraphs and BB-Ref uses BIS Defensive Runs Saved as the basis for their defensive contribution to WAR.

However, I have been digging into this recently and noticed that the DRS numbers are different in the two places.

Here’s an image of an Excel table showing team data for both 2018 and 2019:

https://i.imgur.com/KQMZDjo.png

BR = DRS numbers from BB-Ref
FG = DRS numbers from Fangraphs
FG nrm = Fangraphs normalized so that the MLB average is zero
diff = (FG nrm) - BR

And here is a plot of FG nrm vs. BR for both years.  Obviously, the FG nrm and BR data are correlated:

https://i.imgur.com/dwfQs0l.png

Anybody know why they are different?

(Sorry I couldn’t figure out how to embed the images.)

Actually, I have a small mistake… Fangraphs uses UZR in their WAR formulation, whereas BB-Ref’s WAR calculation uses DRS from 2003 onward.

Nonetheless, both sites have different DRS numbers.

It’s probably the “shift” runs.  Check the “rTS” column and remove that from DRS.

Thanks! (Though I should have found it myself! 😊 )

That seems to be it, though it doesn’t fully cover the discrepancy.  I’ll look at a few more years and summarize.