RedBird Capital Partners, a private equity firm, agreed to acquire an 11% stake in Boston Red Sox, a baseball club. Separately, LeBron James has acquired around a 1% stake in the club, although without investing any new money. Financial terms were not disclosed. With the deal for Fenway Sports, RedBird Capital has pushed private equity into US pro sports team ownership, a space the niche asset class has long sought but rarely entered. And that should provide a boon for a PE industry that touts its ability to make money during a market downturn.