At least one big trader is buying puts in the IYT exchange traded fund, looking for the transport sector to take a dive.

's tracking systems detected the purchase of 10,000 August 46 puts for $0.70 and $0.75 against open interest of just 56 contracts this morning in the iShares Dow Jones Transportation Average ETF. The transaction was 14 times larger than the average daily options volume in the name.