Hedge funds earn positive ex post abnormal returns and avoid negative abnormal returns on their equity portfolios when trading in the opposite direction of highly diversified low-turnover institutional investors (quasi indexers). This pattern seems to be driven by the preferences of quasi indexers for high-market-beta stocks together with the ability of hedge funds to identify subsets of especially profitable trades. It remains pronounced when accounting for other determinants of hedge fund trades, such as stock liquidity, market anomalies, and major corporate events. Trading against other institutional investors or noninstitutions does not result in abnormal performance for hedge funds. This paper was accepted by David Sraer, finance. Supplemental Material: Data and the online appendix are available at https://doi.org/10.1287/mnsc.2023.4877 .