George Soros built a big bet at the end of last year that the stock market was due for a tumble.

Mr. Soros’s hedge fund, Soros Fund Management LLC, boosted its so-called “put” position on the exchange traded fund market’s biggest and most widely traded fund, the SPDR S&P 500 ETF, known by its ticker symbol SPY. The ETF tracks the broad S&P 500 stock index.