diff --git a/tests/unit/playerGrouping.test.js b/tests/unit/playerGrouping.test.js
new file mode 100644
index 0000000..05b67cb
--- /dev/null
+++ b/tests/unit/playerGrouping.test.js
@@ -0,0 +1,70 @@
+'use strict';
+
+// P0-3 — player/market grouping. Same player must present as ONE row per market
+// family (alt lines nested), and no single market may flood a ranked list.
+
+const { dedupeLeaders, groupIntoLadders, marketFamily } = require('../../web/src/lib/playerGrouping');
+
+describe('dedupeLeaders', () => {
+  test("collapses a player's alt-line ladder to ONE leaderboard row (Bohm strikeouts)", () => {
+    const rows = [
+      { player: 'Alec Bohm', stat: 'strikeouts', line: 1.6, side: 'U', grade: 'B' },
+      { player: 'Alec Bohm', stat: 'strikeouts', line: 1.3, side: 'U', grade: 'B' },
+      { player: 'Alec Bohm', stat: 'strikeouts', line: 1.5, side: 'O', grade: 'B' },
+      { player: 'Mike Trout', stat: 'hits', line: 0.5, side: 'O', grade: 'A' },
+    ];
+    const out = dedupeLeaders(rows);
+    expect(out).toHaveLength(2);
+    expect(out[0]).toMatchObject({ player: 'Alec Bohm', line: 1.6 }); // first (best-ranked) kept
+    expect(out[1].player).toBe('Mike Trout');
+  });
+
+  test('caps a flooding market so 9 identical stolen_bases rows do not dominate', () => {
+    const rows = Array.from({ length: 9 }, (_, i) => ({ player: `Runner ${i}`, stat: 'stolen_bases', line: 0.5, side: 'U', grade: 'B' }));
+    rows.push({ player: 'Slugger', stat: 'home_runs', line: 0.5, side: 'O', grade: 'A' });
+    const out = dedupeLeaders(rows, 4);
+    expect(out.filter((r) => r.stat === 'stolen_bases')).toHaveLength(4); // capped
+    expect(out.some((r) => r.stat === 'home_runs')).toBe(true);          // other markets survive
+  });
+
+  test('name variants merge (accents/nicknames) — no double entry', () => {
+    const out = dedupeLeaders([
+      { player: 'José Ramírez', stat: 'total_bases', line: 1.5 },
+      { player: 'Jose Ramirez', stat: 'total_bases', line: 2.5 },
+    ]);
+    expect(out).toHaveLength(1);
+  });
+
+  test('empty / malformed → empty, no throw', () => {
+    expect(dedupeLeaders(null)).toEqual([]);
+    expect(dedupeLeaders([{}])).toEqual([]);
+  });
+});
+
+describe('groupIntoLadders', () => {
+  test('nests alt lines under one player+market entry, rungs sorted by line', () => {
+    const groups = groupIntoLadders([
+      { player: 'Alec Bohm', stat: 'strikeouts', line: 1.6, grade: 'B' },
+      { player: 'Alec Bohm', stat: 'strikeouts', line: 1.3, grade: 'A' },
+      { player: 'Alec Bohm', stat: 'strikeouts', line: 1.5, grade: 'B' },
+    ], (a, b) => (b.grade < a.grade ? b : a)); // pick the best grade as primary
+    expect(groups).toHaveLength(1);
+    expect(groups[0].ladder.map((r) => r.line)).toEqual([1.3, 1.5, 1.6]); // rungs ascending
+    expect(groups[0].primary.grade).toBe('A'); // betterOf picked the A rung
+  });
+
+  test('different markets for the same player stay separate ladders', () => {
+    const groups = groupIntoLadders([
+      { player: 'X', stat: 'hits', line: 0.5 },
+      { player: 'X', stat: 'total_bases', line: 1.5 },
+    ]);
+    expect(groups).toHaveLength(2);
+  });
+});
+
+describe('marketFamily', () => {
+  test('strips case/space; side+line are not part of the family', () => {
+    expect(marketFamily('Total Bases')).toBe('total_bases');
+    expect(marketFamily('stolen_bases')).toBe('stolen_bases');
+  });
+});
diff --git a/web/src/components/ExploreHub.tsx b/web/src/components/ExploreHub.tsx
index 0baf0ad..e338431 100644
--- a/web/src/components/ExploreHub.tsx
+++ b/web/src/components/ExploreHub.tsx
@@ -4,6 +4,7 @@ import { useEffect, useMemo, useState } from 'react';
 import SportBadge from '@/components/vyndr/SportBadge';
 import GradeBadge from '@/components/vyndr/GradeBadge';
 import { playerHref } from '@/lib/playerHref';
+import { dedupeLeaders } from '@/lib/playerGrouping';
 
 /**
  * ExploreHub (Session 42 leaders; Session 60 night2/C — THE AGGREGATOR).
@@ -54,7 +55,11 @@ export default function ExploreHub() {
 
   const rows = useMemo(() => {
     const q = query.trim().toLowerCase();
-    return q ? leaders.filter((l) => (l.player || '').toLowerCase().includes(q)) : leaders;
+    const filtered = q ? leaders.filter((l) => (l.player || '').toLowerCase().includes(q)) : leaders;
+    // P0-3 — ONE row per player+market family + a per-market cap, so a player's
+    // alt-line ladder (Bohm ×3) collapses to one entry and no single prop type
+    // (9× stolen_bases) can flood the ranked board.
+    return dedupeLeaders(filtered, 4) as Leader[];
   }, [leaders, query]);
 
   // Wave 2B — never-dark hub. When the selected sport is in its OFF-SEASON, the
diff --git a/web/src/lib/playerGrouping.js b/web/src/lib/playerGrouping.js
new file mode 100644
index 0000000..f8a599b
--- /dev/null
+++ b/web/src/lib/playerGrouping.js
@@ -0,0 +1,86 @@
+'use strict';
+
+/**
+ * Player/market grouping (P0-3) — the phone audit found the same player listed
+ * as separate flat entries everywhere (Bohm's strikeout ladder = 3 ledger cards,
+ * a leaderboard flooded with 9 identical stolen_bases rows). Props must present
+ * as ONE row per player per market family, with alt lines nested as a ladder,
+ * and no single market may flood a ranked list.
+ *
+ * CommonJS so it's unit-testable by the plain-JS Jest suite AND importable by
+ * the .tsx surfaces (allowJs) — same doctrine as vyndrTokens / playerName.
+ */
+
+const { nameKey } = require('./playerName');
+
+/** A stat's MARKET FAMILY — alt lines of the same market collapse together.
+ *  (Side/line are stripped; only the stat type identifies the family.) */
+function marketFamily(stat) {
+  return String(stat || '').trim().toLowerCase().replace(/\s+/g, '_');
+}
+
+function playerMarketKey(player, stat) {
+  return `${nameKey(player)}|${marketFamily(stat)}`;
+}
+
+/**
+ * Dedupe ranked leaderboard rows: ONE row per (player, market family) — keeping
+ * the FIRST (best-ranked) occurrence — then a per-market cap so one prop type
+ * can't flood the board. Input order is preserved (callers pass pre-ranked).
+ *
+ * @param {Array<{player?:string, stat?:string}>} rows
+ * @param {number} [perMarketCap=4] max rows of one market family on the board
+ * @returns {Array} deduped, capped, order-preserving
+ */
+function dedupeLeaders(rows, perMarketCap = 4) {
+  const seen = new Set();
+  const marketCount = new Map();
+  const out = [];
+  for (const r of Array.isArray(rows) ? rows : []) {
+    if (!r || !r.player) continue;
+    const key = playerMarketKey(r.player, r.stat);
+    if (seen.has(key)) continue;                 // one row per player+market
+    const fam = marketFamily(r.stat);
+    const n = marketCount.get(fam) || 0;
+    if (perMarketCap > 0 && n >= perMarketCap) continue; // don't let one market flood
+    seen.add(key);
+    marketCount.set(fam, n + 1);
+    out.push(r);
+  }
+  return out;
+}
+
+/**
+ * Group flat prop rows into ONE entry per (player, market family) with the alt
+ * lines nested as a ladder — the Alt Line Ladder shape (the /pricing Desk demo).
+ * `betterOf(a, b)` picks the primary/base line (default: keep the first seen).
+ * Order of first appearance is preserved.
+ *
+ * @param {Array} rows  each { player, stat, line, ... }
+ * @param {(a,b)=>any} [betterOf] choose the representative row of a ladder
+ * @returns {Array<{ player, stat, market, primary, ladder }>}
+ */
+function groupIntoLadders(rows, betterOf) {
+  const byKey = new Map();
+  const order = [];
+  for (const r of Array.isArray(rows) ? rows : []) {
+    if (!r || !r.player) continue;
+    const key = playerMarketKey(r.player, r.stat);
+    if (!byKey.has(key)) {
+      byKey.set(key, { player: r.player, stat: r.stat, market: marketFamily(r.stat), primary: r, ladder: [r] });
+      order.push(key);
+    } else {
+      const g = byKey.get(key);
+      g.ladder.push(r);
+      if (typeof betterOf === 'function') g.primary = betterOf(g.primary, r);
+    }
+  }
+  // Sort each ladder by line ascending for a stable rungs display.
+  for (const key of order) {
+    const g = byKey.get(key);
+    g.ladder.sort((a, b) => (Number(a.line) || 0) - (Number(b.line) || 0));
+  }
+  return order.map((k) => byKey.get(k));
+}
+
+module.exports = { marketFamily, playerMarketKey, dedupeLeaders, groupIntoLadders };