Because traders try to close or roll over their positions, trading volume is usually above average on quadruple witching, which can lead to greater volatility. But one interesting phenomenon is that the price of a security may artificially tend toward a strike price with large open interest as gamma hedging takes place, a process called pinning the strike. Pinning a strike imposes pin risk for options traders, where they become uncertain whether or not they should exercise their long options that have expired at the money, or are very close to being at the money. This happens because they are also unsure of how many of their similar short positions they will be assigned on at the same time.