The stock market had its biggest one-day drop since February on Thursday as the disappointing earnings from Apple (AAPL) and a weak 1st quarter advance reading on GDP added to the overnight selling pressure. The futures had dropped in reaction to the lack of BOJ action. After the close Thursday the market got a positive surprise as Amazon.com (AMZN) and LinkedIn (LNKD) both beat earnings in impressive fashion.
It appears that some traders had apparently bet heavily on more easing by the BOJ so the unwinding of these large new long positions likely accentuated the selling.