Shares of AMC Entertainment (NYSE: AMC) plummeted 57% yesterday, a big setback to a week that had seen a short squeeze send the stock soaring over 800%. Similarly, GameStop (NYSE: GME) tumbled 44%, ending a multi-day rally that had allowed to quadruple in value. While there has always been tension between short-sellers and investors who are long holders of a stock, the recent battle of wills began when some investors on Reddit noticed hedge funds had placed enormous bets that GameStop's stock price would fall.