108 lines
4.4 KiB
JavaScript
108 lines
4.4 KiB
JavaScript
/**
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* MLB park factors (Session 15).
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*
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* Source: FanGraphs 2024-25 park factor data (three-year weighted
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* average — FanGraphs methodology). Numbers indexed to 100 = league
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* average. Pulled from https://www.fangraphs.com/guts.aspx (Park
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* Factors tab) 2025-04. Update annually; the rolling-three-year
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* window means values move slowly.
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*
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* Fields per park:
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* hr — home run factor (Coors ~128 means HRs are 28% more likely;
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* Oracle/SF ~85 means 15% less likely)
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* h — overall hit factor
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* r — runs factor
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*
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* The feature extractor reads this via `getParkFactor(homeTeam)`
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* during the MLB branch and merges hr/h/r as `park_hr`, `park_h`,
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* `park_r` so the grading engine + reasoning builder can read them
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* without re-doing the lookup.
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*
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* Indexing convention: home-team abbreviation. The road team plays
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* at the home team's park, so a Yankees-at-Angels game uses LAA's
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* park factors regardless of whose batter you're grading.
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*/
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const PARK_FACTORS = Object.freeze({
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// AL East
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BAL: { hr: 109, h: 100, r: 102 }, // Camden Yards — left field wall changes leveled off post-2022
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BOS: { hr: 100, h: 108, r: 106 }, // Fenway — Monster boosts singles/doubles, suppresses HR
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NYY: { hr: 114, h: 101, r: 104 }, // Yankee Stadium — short porch in right
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TB: { hr: 93, h: 96, r: 94 }, // Tropicana — neutral-to-pitcher dome
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TOR: { hr: 106, h: 101, r: 102 }, // Rogers Centre — slight HR boost
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// AL Central
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CHW: { hr: 109, h: 102, r: 105 }, // Guaranteed Rate Field
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CLE: { hr: 96, h: 99, r: 98 }, // Progressive Field — slight pitcher park
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DET: { hr: 90, h: 100, r: 97 }, // Comerica — deep alleys, HR-suppressed
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KC: { hr: 93, h: 103, r: 101 }, // Kauffman — XBH-friendly, HR-neutral
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MIN: { hr: 105, h: 100, r: 101 }, // Target Field
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// AL West
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HOU: { hr: 100, h: 101, r: 101 }, // Minute Maid — Crawford boxes ~neutral, dome
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LAA: { hr: 97, h: 98, r: 98 }, // Angel Stadium
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OAK: { hr: 91, h: 95, r: 92 }, // Coliseum — extreme pitcher park
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SEA: { hr: 96, h: 98, r: 96 }, // T-Mobile Park — marine air
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TEX: { hr: 104, h: 102, r: 103 }, // Globe Life — climate-controlled since 2020
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// NL East
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ATL: { hr: 103, h: 100, r: 101 }, // Truist Park
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MIA: { hr: 89, h: 97, r: 94 }, // loanDepot park — deep alleys
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NYM: { hr: 95, h: 99, r: 97 }, // Citi Field — slight pitcher
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PHI: { hr: 109, h: 100, r: 102 }, // Citizens Bank Park — bandbox right field
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WSH: { hr: 100, h: 100, r: 100 }, // Nationals Park — true neutral
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// NL Central
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CHC: { hr: 106, h: 100, r: 102 }, // Wrigley — wind-driven swings; multi-year average
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CIN: { hr: 113, h: 102, r: 105 }, // Great American — top-3 HR park most years
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MIL: { hr: 104, h: 100, r: 101 }, // American Family Field
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PIT: { hr: 96, h: 101, r: 99 }, // PNC Park — XBH-favorable, HR-suppressed
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STL: { hr: 93, h: 98, r: 96 }, // Busch — neutral-to-pitcher
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// NL West
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ARI: { hr: 100, h: 98, r: 98 }, // Chase Field — humidor since 2018
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COL: { hr: 128, h: 112, r: 120 }, // Coors Field — altitude. Single biggest park effect.
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LAD: { hr: 102, h: 99, r: 99 }, // Dodger Stadium
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SD: { hr: 95, h: 97, r: 95 }, // Petco — marine air pitcher park
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SF: { hr: 85, h: 96, r: 92 }, // Oracle Park — Bay winds suppress HRs heavily
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});
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const NEUTRAL = Object.freeze({ hr: 100, h: 100, r: 100 });
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function normalizeTeamCode(team) {
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if (!team) return null;
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return String(team).trim().toUpperCase();
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}
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/**
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* getParkFactor — lookup by home-team code. Returns null for unknown
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* teams so the feature extractor can drop the signal entirely rather
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* than falsely report "neutral park" on a misspelled abbreviation.
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*
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* @param {string} homeTeam — three-letter team code (BAL, NYY, COL, ...)
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* @returns {{hr:number, h:number, r:number}|null}
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*/
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function getParkFactor(homeTeam) {
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const code = normalizeTeamCode(homeTeam);
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if (!code) return null;
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return PARK_FACTORS[code] || null;
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}
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/**
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* Convenience — when you want a guaranteed object (e.g. arithmetic
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* downstream that can't handle null). Falls back to league-neutral.
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* Prefer getParkFactor + explicit-null branching in code; this is
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* for tests and downstream services that prefer 100s over null.
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*/
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function getParkFactorOrNeutral(homeTeam) {
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return getParkFactor(homeTeam) || NEUTRAL;
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}
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module.exports = {
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PARK_FACTORS,
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NEUTRAL,
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getParkFactor,
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getParkFactorOrNeutral,
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__internals: { normalizeTeamCode },
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};
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