UnitedHealth Group shares jumped as much as 14% on Friday, briefly topping $300, after Berkshire Hathaway disclosed a new position of about five million shares in the health-insurance giant during the second quarter. The purchase, revealed in a regulatory filing late Thursday, marked Berkshire’s first stake in the company since 2017 and helped spark one of UnitedHealth’s biggest single-day gains in decades. Additional hedge-fund filings added to the momentum. David Tepper’s Appaloosa Management lifted its UnitedHealth holding by roughly 1,300% to $764 million, while other large managers, including Two Sigma, also reported fresh or expanded positions. Options activity mirrored the surge in interest, with some $49 million in bullish premium changing hands and 30-day implied volatility rising to 39, still below the upper end of its 52-week range. The renewed buying comes after a punishing stretch for UnitedHealth. The stock had lost about 45% this year amid cyberattack fallout, leadership turnover and earnings disappointments that weighed heavily on the Dow Jones Industrial Average. Investors are now betting that Berkshire’s endorsement and deep-value buying by prominent funds could mark a turning point for the insurer.