Box plus/minus estimates impact from box-score production. RAPM estimates it from what happened while a player was on the floor, holding teammates and opponents fixed. They are answering the same question from different evidence, and RAPM's evidence is closer to the question.
A regression that predicts a player's impact per 100 possessions from his box-score line and his team's performance.
| On-court stints | Box-score totals | |
|---|---|---|
| Input | On-court stints | Box-score totals |
| Needs play-by-play | Yes | No |
| Sees things the box score misses | Yes, in principle | No, by construction |
| Noise on small samples | High; shrunk toward a box-score prior | Low, because the box score is stable |
This site uses RAPM, and uses a box-score prior to shrink it where possessions are thin, which is an attempt to take the strengths of both. On a full season of possessions prefer RAPM; on a few hundred prefer the prior.
Neither is causal, and neither can separate a player from the lineups he happened to play in.
Definitions: Net RAPM.
Over Expected is a basketball shot-value platform covering NBA, EuroLeague, EuroCup, Liga ACB, Lega Basket Serie A, Basketball Bundesliga, Greek Basket League, ABA Liga, WNBA.