One week ago, and again last night, we previewed today's main event: an immensely important quad-witching expiration, the year's last, one which as JPM's head quant calculated will be 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."
What is most important, is that the "pin risk", or price toward which underlying prices may gravitate if HFTs are unleashed to trigger option stop hunts, is well below current S&P levels: as JPM notes, "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."
What does this mean? Considering that the bulk of the puts have been layered by the program traders themselves, including CTA trend-followers and various momentum strategist (which work in up markets as well as down), and since the vol surface of today's market is well-known to everyone in advance, there is a very high probability the implied "stop loss" level will be triggered.
Not helping matters will be the dramatic lack of market depth (thank you HFTs and regulators) and overall lack of liquidity, which means even small orders can snowball into dramatic market moves. "While equity volumes look robust, market depth has declined by more than 60% over the last 2 years. With market depth so low, the market does not have capacity to absorb large shocks. This was best illustrated during the August 24th crash."
That's the qualitative explanation. What about the quantitative? According to Thomson Reuters data, between SPX 2050 and 1900 levels there are currently about 1.1 mln put contracts open vs 739,000 call contracts. As Reuters unnecessarily observes, "unless there is a substantial move in either direction that is sharply greater than the standard deviation, large SPX options positions should have limited impact on the market."
Well of course: the problem is that since over the past 7 years, the entire market has become one giant stop hunt, the very algos which "provide liquidity" will do everything they can to inflict the biggest pain possible to option holders - recall that for every put (or call) buyer, there is also a seller. As such, illiquid markets plus algo liquidity providers makes for an explosive cocktail at a time when the Fed is already worried whether the Fed may have engaged in "policy error."
So what does this mean in simple English? As Reuters again points out, levels to watch are the large imbalances in favor of puts in Dec SPX put contracts at 2050, 2000, 1950, 1900 strikes
It further writes that "as SPX moves below these levels market makers who are short these puts would be forced to sell spot futures to hedge, which could exacerbate a market selloff."
In other words, selling which begets even more selling, which begets even more selling.
The Fed's trading desk, and its Citadel "market supportive" joint venture, will be busy.