Cross-venue signal, hedged long-short execution. For 11 liquid alts (LINK, AVAX, DOT, ATOM, NEAR, FIL, ADA, LTC, UNI, AAVE, INJ) compute the daily spot volume share = spot_volume(<ALT>USDT.BINANCE_SPOT) / (spot_volume + perp_volume(<ALT>USDT.BINANCE)), both in base units from 1-DAY bars. A 3-day mean of the share is z-scored against the prior 60 days, lagged 3 days so the event window is excluded. An event is a 3-day alt log return MINUS the BTC perp 3-day log return below -move_k * sigma_daily(30d) * sqrt(3) while share_z > share_z_entry. The relative selloff came through the spot book rather than leveraged perps. That points to holders, unlock recipients or treasuries dumping inventory, which is non-informational and pushes price below where derivatives traders value the coin. Perp-led selloffs carry information (leveraged shorts, liquidations) and do NOT rebound in the pre-study. On each event: buy the alt perp and short an equal dollar amount of BTCUSDT.BINANCE, so the trade is beta-neutral to the crypto market, and hold for hold_days. PRE-STUDY (run 2026-10-02 on local catalog daily bars, 2020-2026, 11 coins, gross and before costs): 142 events at k=1.5, z>1. Mean 3-day BTC-relative return +2.51% (overlap-adjusted t 2.08), positive in every calendar year 2021-2026 (2021 +3.7%, 2022 +0.3%, 2023 +2.1%, 2024 +4.2%, 2025 +1.6%, 2026 +1.8%). The only losing year was 2020, with a few events at -4.6%. Controls: perp-led relative selloffs (share z<-1) +0.74% (t 0.49); perp-led relative rallies faded -0.24%; the mirror 'spot-led rally continuation' worked only in 2021 and lost in 2024-2026, so it was rejected and is NOT part of this hypothesis. The edge sits where the market observation (venue composition of selling) differs, not in a calendar or a funding/OI gate. Data: BinanceVisionCollector klines for both BINANCE (USD-M) and BINANCE_SPOT. All 23 1-DAY bar series were verified present in data/catalog: perps from 2020-01 (LINK, ATOM) through 2020-09 (AVAX), spot from 2019-2020, all through 2026-10-01. Daily bars keep the run at about 55k bars total, well inside the sandbox budget. Risk: 12% of equity notional per alt leg plus an equal BTC hedge leg, at most 4 concurrent events (96% gross long + 96% gross short at 2x account leverage), one open event per coin.