Hedge fund managers sold borrowed gamestop stock, betting it would go down, at which point it would buy it back so they could could return it and keep the difference. Small investors saw what was happening and bought up as much stock as they could, increasing the demand and driving the stock through the roof. Hedge fund looses billions because it cost so much to replace borrowed stocks that skyrocketed. Also, they shorted excess of 100% of their stock (140%). They were attempting to manipulate the market and got caught with their pants down.