When the value of some exchange-traded funds fell more than the indices they were tracking in August, a group of hedge funders saw an affirmation — that ETFs are vulnerable. ETFs are made up of baskets of securities and are seen as a cheap means of gaining broad exposure to markets. The US ETF industry had nearly $2 trillion in assets under management at the end of 2014. Some hedge funds are now betting that some ETF price swings "are more pronounced than the moves of their underlying assets," according to The Wall Street Journal. Steven Cohen of Point72 has been betting against commodities...