Think October 1987, Fatal Attraction (MD precursor to Wall Street, Twinkies World Series bid and then......
Spy OCT Puts 100 strike has 386 000 open interest. I'm not very savy with options. That being said , does that much open interest on the puts at 100 mean that someone is betting a lot of money that we fall hard in oct?
Open interest are contracts that haven't been settled. There could be a lot of traders making small bets, not necessarily anyone making large bets. Wiki: "For each buyer of a futures contract there must be a seller. From the time the buyer or seller opens the contract until the counter-party closes it, that contract is considered 'open'."