Downside price gaps (open versus prior close) represent Skynet's inability to manage the futures market - usually attempting to have a seamless price flow from day to day. My theory is that this is due to the strong linkage to the Yen carry trade (RISK OFF).
These are all of the S&P (SPY) downside gaps (absolute value) since 2009. The biggest gap was on August 24th when the S&P opened down 100 points (10 SPY points). The second largest gap in seven years was this past Friday.
The top 5 largest gaps are all since August 24th:
The top 5 largest gaps are all since August 24th: