Identifies fantasy baseball players whose surface stats (wOBA, ERA, batting average) are diverging from their underlying Statcast quality (xwOBA, FIP, xBA) — emits a `regression_index` from -100 (very lucky, sell high) to +100 (very unlucky, buy low). Primary signal for buy-low/sell-high decisions on trades and waivers. Use when user mentions "buy low", "sell high", "regression candidate", "lucky", "unlucky", "xwOBA gap", "ERA-FIP gap", "BABIP", "due for regression", or is deciding whether to trade for / trade away a player based on over- or under-performance.
Scenario: User asks "Is Junior Caminero a buy-low candidate or am I chasing noise?"
Raw data gathered from Baseball Savant + FanGraphs (cite URLs):
Regression index calculation:
regression_index = (xwOBA - wOBA) x 500
= (.380 - .310) x 500
= +35
Secondary check — BABIP: .255 is below the .240 lower-outlier threshold for hitters only if we tighten further, but .255 plus elite contact quality confirms unlucky. Not a "will correct to .300" player, but unlikely to stay at .255 given the batted-ball profile.
Verdict: regression_index = +35 → BUY. Caminero has been unlucky; underlying contact quality is elite. Expect his surface stats to catch up over the next 30 days.
User-facing translation (per CLAUDE.md rule #5 — beginner writing):
"Junior Caminero's raw numbers look mediocre (.310 wOBA — that's a catch-all hitting stat), but the quality of his actual contact (how hard and at what angle he hits the ball) suggests he should be hitting .380. The gap is one of the biggest in the league. ADD if available, or OFFER a trade for him before his stats correct."
Signal file emission (per signal-framework.md):
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