Hedge fund giants Steve Cohen and Ken Griffin are joining forces to bail out a fellow trader whose positions in runaway stocks like GameStop have been getting hammered. Griffin’s Citadel and Cohen’s Point72 Asset Management are investing a combined $2.75 billion into Melvin Capital Management, which has seen its recent bets on stock declines thwarted by a small army of investors with get-rich-quick dreams. The fund, run by ex-Cohen lieutenant Gabe Plotkin, is down 30 percent, the Wall Street Journal reported.