The most popular way for investors to trade small caps is through the iShares Russell 2000 ETF (IWM).  IWM averages nearly 30 million shares traded per day, and over 750,000 options. Last week, a large fund or trader placed a block of nearly 50,000 puts in IWM that expire in October. These far-out-of-the-money puts could be a hedge against a major selloff in small caps.