# OPPORTUNITY_DRIFT AXIS — BUILT, LIVE AS A CHALLENGER, PROOF PENDING

**Date:** 2026-08-01 · champion `p_win` and the live grade path **byte-identical** ·
ledger-only challenger · queries committed (`scripts/opportunity-axis-holdout.sql`).

**Gates:** 4,073 tests / 326 suites green · `next build` exit 0 · input mapped ·
coverage measured · **collinearity guard PASSED** · axis writing on prod.

---

## STEP 1 — INPUT MAPPED, AND MEASURED

`MLB_LOG_FIELD` now maps `at_bats → 'atBats'`.

**Deliberately NOT added to the other two MLB maps** (`outcomeService`'s
`MLB_LOG_FIELD`, `liveTrackingService`'s `LIVE_BOX_FIELD`). Those exist to
**settle** and **track** graded props; nothing grades at-bats, so adding it there
would imply a settlement path for a market we do not carry. A test asserts the
settle map still lacks it.

### Coverage on real props (n=100, MLB)

| feature | coverage |
|---|---:|
| `opportunity_drift` | **94%** |
| `recent_ab_per_game` | 94% |
| `ab_per_game` | 94% |

By stat — and the split is exactly what it should be:

| stat | n | drift |
|---|---:|---:|
| `total_bases` | 42 | **100%** |
| `hits` | 36 | **100%** |
| `home_runs` | 8 | **100%** |
| `strikeouts` | 5 | 40% |
| `outs` / `earned_runs` / `hits_allowed` | 3 each | 66.7% |

**Batters 100%, pitchers partial** — correct: pitchers accumulate few at-bats, so
the drift is genuinely undefined for many of them and **abstains** rather than
inventing a ratio.

---

## STEP 2 — 🟢 THE COLLINEARITY GUARD PASSES DECISIVELY

This was the gate that could have killed the axis before it was worth building.

| correlation | n | r |
|---|---:|---:|
| `drift` vs `l20_avg` | 94 | **−0.020** |
| `drift` vs `l5_avg` | 94 | **+0.027** |
| `drift` vs `ab_per_game` | 94 | **−0.029** |

**All three are essentially zero.** The drift ratio is **orthogonal to every
existing projection input** — it carries information the projection does not
already contain.

**This also validates the ratio-over-level decision empirically.** `ab_per_game`
(the level) is the same quantity divided by the same denominator as `l20_avg`;
had we used it, we would have added a redundant input. **Dividing by the player's
own baseline removed the collinearity** — r = −0.029 against the very quantity it
is built from.

---

## STEP 3 — THE AXIS IS LIVE AS A CHALLENGER

`opportunityNudge` composes in the same log-odds space as park and platoon
(`log` of a ratio), with **two guards the measured axes do not get**:

- **A ±10% deadband.** A rest day, a pinch-hit appearance or a blowout can move a
  5-game window without any change in role.
- **A tighter cap — 0.15 vs the environment's 0.30.** This is a *proxy*, not a
  measurement, and a noisy proxy must not outvote measured signals.

Every adjustment carries **`is_proxy: true`** and
**`proxy_for: 'confirmed_batting_order'`**, so nothing downstream can mistake it
for a lineup feed.

The axis can **stand alone** — without that, the challenger's early return would
have gated opportunity off on exactly the thin-classification rows it is most
likely to help.

**Zero extra I/O:** `analyzeViaEngine1` attaches drift from the feature vector it
has already built; `attachChallenger` reads it off the grade. Nothing re-fetches
in a loop running over hundreds of props.

### Verified writing on prod (induced snapshot, 416 grades)

| | |
|---|---:|
| rows with a challenger value | 275 / 276 |
| **rows carrying the opportunity axis** | **142 (51.4%)** |
| rows where the challenger moved | 190 |
| mean \|delta\| when it moved | **0.034** |
| delta range | −0.089 … +0.108 |

**Champion `p_win` unchanged. Live grade path unchanged.** The axis writes only
to `p_win_challenger` / `challenger_adjustments`.

---

## STEP 4 — ⏳ HOLDOUT PROOF IS n-BLOCKED BY CONSTRUCTION

```
settled MLB rows (all):                         605
settled rows with a challenger value:           250
settled rows carrying the OPPORTUNITY axis:       0
first game_date carrying the axis:       2026-08-01  (tonight — not yet played)
```

**The axis went live today. Its first rows are on games that have not happened.**
No holdout can be run, and **I am not going to manufacture one** — running the
test on rows the axis never touched would dilute the comparison with rows where
challenger ≡ champion by construction, and **make a null result look like a small
positive one.**

**Earliest possible run:** tomorrow's settle pass. **Defensible n:** several days,
at ~140 axis-carrying rows per snapshot.

The query is written and committed (`scripts/opportunity-axis-holdout.sql`). It
filters to `challenger_adjustments LIKE '%opportunity%'` for exactly the reason
above, buckets before measuring reliability, and splits time-forward.

**BOTH reliability and resolution must improve. One or neither → SHELVE.**

---

## STEP 5 — NOT REACHED

Nothing promoted. Nothing flipped. The axis sits in the ledger accruing evidence.

## THE PROXY CAVEAT, CARRIED FORWARD

**This is a proxy for tonight's batting order, not a measurement of it.** The real
input is the confirmed lineup slot, which no wired source exposes
(`depthChartService` returns `battingOrder: null` for MLB; PropLine `/context`
carries only a `lineup_confirmed` boolean). **If a lineup feed becomes available,
this axis should be replaced by the real slot, not supplemented with it.**

## A MEASUREMENT TRAP WORTH RECORDING

The first prod coverage run reported **`opportunity_drift` at 0%** while
`ab_per_game` read 94% — which looks exactly like "the feature does not compute".

It was the **120-second feature-vector cache** (`VECTOR_TTL_SECONDS`): the probe
ran inside the window and read payloads written by the previous image, which had
no such field. Re-running past the TTL gave 94%.

**A new feature field is invisible for one cache generation after deploy.** Worth
knowing before concluding a feature is broken — I very nearly reported this one
as absent, having already confirmed against the live statsapi payload that
`atBats` was present and that the code produced `drift = 1.05` locally on that
exact data. **The contradiction between those two facts is what saved it.**