Trader could lose more than $500 million on a single position if S&P 500 tumbles By: MarketWatch January 15, 2019 at 11:32 AM EST If the S&P drops below 2,100 by the end of next year, one trader will face a costly — and now, high-profile — reckoning. Read More >> Related Stocks: Berkshire Hathaway Nasdaq Composite