See, investors bet on Volkswagen's share price going down, partially because Porsche said it wasn't going to attempt a takeover. But Porsche was attempting to take over VW, having bought up nearly 75-percent of VW's publicly traded shares. When word broke that Porsche owned nearly three-quarters of VW (which indicated an imminent takeover attempt), rather than go down like the hedge funds bet it would, VW's share price skyrocketed to over 1,000 euros per share, according to Reuters.
Naturally, when you bet that a company's share price is going to drop and it in turn (temporarily) becomes the world's most valuable company, you lose a lot of money, unless you're able to buy up shares before prices jump too much. This led to a squeeze on the stock, which the hedge funds accuse Porsche and Piëch (who are both members of the Porsche family and supervisory board) of organizing.
"Porsche SE and its supervisory board members will defend themselves with all available legal means," a Porsche statement said. This is the second suit against the company, following a case that's pending in Hannover. A similar case was filed in New York, but was later dismissed.