Curious why someone just pulled a trapdoor from under the market? JPM's Marko Kolanovic, head of quant strategies explains.
Impact of option hedging on the S&P 500 into the close
S&P 500 put option gamma exceeded call option gamma by more than $50bn prior to the option expiry this morning. This was the highest S&P 500 put gamma imbalance ever. The impact of this imbalance was evident in the intraday market momentum developed from 3:30PM to the close yesterday. The Figure below left show yesterday’s intraday price action for the S&P 500. We note that the market selloff accelerated into the close, with a 60bp fall in the last 30 minutes. Consistent with theory on the impact of gamma hedging (see our report Impact of Derivatives Hedging), this temporary market impact reversed near the market open today (57bps recovery in the first 30 minutes, right Figure).
Despite the fact that S&P 500 options expired this morning, put gamma is still higher than call gamma by ~$38bn, which is a large imbalance (on account of other S&P 500 option maturities and SPY options expiring at the close). This can lead to further selling pressure into the close today.
Given that the market is already down ~2%, we expect the market selloff to accelerate after 3:30PM into the close with peak hedging pressure ~3:45PM. The magnitude of the negative price impact could be ~30-60bps in the absence of any other fundamental buying or selling pressure into the close.