NAIL-RAPM v1.2.1: Pruned Non-Additive Context
NAIL-RAPM v1.2.1 is a controlled ablation of the production v1.2 gap-returner model. It retains all eight additive profile totals, the value-conditioned aging prior, exposure-gated cold starts, gap-returner bridge, stat-specific profile padding, and Ridge regularization. It removes four of v1.2's six non-additive lineup-context terms.
Feature Contract
| v1.2 non-additive term | v1.2.1 |
|---|---|
| Usage concentration | Retained |
| Top-two assists | Retained |
| Bottom-two three-point makes | Removed |
| Credible shooter count | Removed |
| Shooting-by-usage | Removed |
| Shooter-by-passing | Removed |
The selection is based on the v1.2 coefficient audit: usage concentration has the same positive sign in every completed source season, while top-two assists is positive in 89.7%. The four removed terms are directionally unresolved over the historical panel. This is a feature-selection hypothesis, not a claim that the removed concepts are unimportant in basketball.
Retained-Term Trajectories
Each panel below is a standardized Ridge coefficient from one completed source season. It estimates the conditional change in a home-minus-away stint rating for a one-standard-deviation increase in that five-man feature, holding the eight additive profile totals and the other retained non-additive term fixed. These are lineup-context coefficients, not player ratings or causal effects.
There are 29 fitted source-season states because the first historical season
has no prior context state. usage_concentration is positive in all 29, with a
median standardized coefficient of +0.91 and mean absolute coefficient of
0.89. top_two_assists is positive in 26 of 29 (89.7%), with median +0.59 and
mean absolute coefficient 0.69. The chart also makes the remaining uncertainty
visible: top-two assists has a wider historical range (-0.67 to +2.32), so its
retention rests on strong directional consistency rather than a claim of a
time-invariant effect size.
Additive Profile Trajectories
The eight additive player-profile totals are unchanged from v1.2 and remain eligible for exact player-level attribution. Their fitted weights are not, however, mechanically identical: the Ridge model refits all ten retained coordinates jointly after the four non-additive terms are removed. The chart therefore shows the v1.2.1 weights themselves rather than reusing v1.2's fourteen-term fit.
Across the 232 matched feature-season coefficients, the v1.2 and v1.2.1 additive weights have Pearson correlation 0.967 and mean absolute change 0.126 standardized units. The largest changes are in three-point attempts and makes, which is expected because the removed terms explicitly involved shooting. The remaining additive contract is therefore broadly stable, but not identical.
Frozen Results
The recursive fit uses all 30 completed seasons. The strict three-season replay forecasts 2023-24, 2024-25, and 2025-26 from each season's preseason information set. v1.2 is the direct incumbent.
| Model | Poss. RMSE | Eligible game RMSE | Full-game RMSE | Winner accuracy | Team NetRtg RMSE | Pythagorean-win RMSE | Playoff eligible-game RMSE |
|---|---|---|---|---|---|---|---|
| NAIL-RAPM v1.2 | 1.197958 | 14.0414 | 14.2660 | 68.16% | 3.2908 | 7.0899 | 16.6148 |
| NAIL-RAPM v1.2.1 | 1.197952 | 14.0246 | 14.2521 | 68.24% | 3.2706 | 7.0351 | 16.5942 |
The candidate lowers the pooled full-game RMSE by 0.0139 points. It also has slightly lower playoff possession RMSE (1.192709 versus 1.192734) and playoff eligible-game RMSE (16.5942 versus 16.6148). These are small changes, so the decision uses the predeclared paired game-block bootstrap rather than the point estimates alone.
Differences below are v1.2.1 minus v1.2: negative values favor the pruned candidate. The predefined non-promotion gate permits an upper 95% bound no larger than 0.5% of the incumbent full-game RMSE in every scope.
| Scope | Full-game RMSE difference | Paired 95% interval | Gate threshold | Gate |
|---|---|---|---|---|
| Pooled | -0.0139 | [-0.0304, +0.0028] | +0.0713 | Pass |
| 2023-24 | +0.0149 | [-0.0031, +0.0325] | +0.0697 | Pass |
| 2024-25 | -0.0593 | [-0.1022, -0.0142] | +0.0722 | Pass |
| 2025-26 | +0.0024 | [-0.0146, +0.0209] | +0.0720 | Pass |
Decision
v1.2.1 clears the agreed non-promotion gate in the pooled replay and each target season. It is the new regular-season leader in the three-season frozen table while using four fewer non-additive terms. The website bundle remains on v1.2 until this candidate is explicitly promoted for deployment.
Artifacts
- Recursive candidate:
artifacts/models/forward_nail_rapm_v121_pruned_nonadditive/2025-26/forward-nail-rapm-v121-pruned-nonadditive-2025-26-20260822T171824Z-bd4da5c4 - Frozen replay:
artifacts/models/nail_v121_pruned_nonadditive_frozen_backtest/frozen_multiseason_backtest/2023-24_to_2025-26/frozen_multiseason_backtest-2023-24-to-2025-26-20260822T202752Z-d470f6d9 - Paired bootstrap:
artifacts/models/nail_v121_pruned_nonadditive_bootstrap/2023-24_to_2025-26/nail-v121-pruned-nonadditive-bootstrap-20260822T202828Z-d42bb340 - Coefficient audit:
artifacts/models/analysis/nail_v121_pruned_nonadditive_weight_audit/nail-v121-pruned-nonadditive-weight-audit-20260822T204159Z-0c9436cd