Is This What Happens On Monday?
This important event falls at a peculiar time—less than 48 hours before the largest option expiry in many years. There are $1.1 trillion of S&P 500 options expiring on Friday morning. $670Bn of these are puts, of which $215Bn are struck relatively close below the market level, between 1900 and 2050. Clients are net long these puts and will likely hold onto them through the event and until expiry. At the time of the Fed announcement, these put options will essentially look like a massive stop loss order under the market.
Source: zerohedge.com