Short selling is booming again after almost being left for dead due to the GameStop mania, reviving hope that hedge funds could turn things around in 2021. Hedge funds' short book generated in July the best alpha since 2010, and now it's outperforming the long side of their strategies, according to Morgan Stanley prime brokerage data. The rebound came after a tough start to the year when the monstrous GameStop short squeeze inflicted huge pain for short sellers betting against the brick-and-mortar retailer.