Method · era_minus_xera@v1

ERA minus expected ERA

The gap between what a pitcher's earned run average actually was and what Statcast expected it to be from the quality of contact he allowed, his strikeouts and his walks. A positive gap means he pitched better than his ERA says. A negative gap means his ERA flattered him.

The filter, exactly as it runs

era IS NOT NULL AND xera IS NOT NULL

Where this is arguable

xERA assumes league-average defense and sequencing. A pitcher in front of a bad defense is penalised by his real ERA and rescued by this one, and neither is the whole truth.
It says nothing about durability. A pitcher whose xERA is excellent over 60 innings is not the same asset as one who threw 170.
One season of gap is mostly noise plus a little signal. The signal is worth acting on only when the underlying inputs agree.

These are the objections I already know about. If you have a better one, or you think a different threshold tells a truer story, say so and I will re-run it with your numbers and publish what comes back.

Version 1. Older versions are never deleted, so a piece that citesera_minus_xera@v1 stays reproducible after this definition is revised. Source: Data: nflverse (nflfastR), CC-BY 4.0