Volatility plumbing: gamma moves

A stock can drop 2% in an hour with no earnings miss, no Federal Reserve speech, and no war headline because a big part of the move is sometimes coming from the options market itself, not from investors changing their view of the company. Cboe says gamma hedging can force dealers to keep buying or selling futures as prices move, which can magnify an intraday swing. (cboe.com) An option is a contract tied to a stock or index, and the United States Securities and Exchange Commission says listed options are traded on securities marketplaces and can be used for hedging or speculation. That matters because every option trade creates a second trade somewhere else by the firm taking the other side. (investor.gov) That second trade is called a hedge, and it works like a store owner restocking shelves after customers buy too much of one item. If a dealer sells call options that gain value when the market rises, the dealer often buys stock or futures to offset that exposure. (cboe.com) Delta is the first piece of this plumbing, and it means how much an option’s price tends to move when the underlying stock or index moves by $1. Gamma is the second piece, and Cboe defines it as the change in that delta as the underlying price changes. (cboe.com) Gamma is why hedging can speed up right when the tape gets jumpy. If delta is the steering wheel angle, gamma is how fast the wheel keeps turning while the car is already in the curve. (cboe.com) When dealers are short gamma, Cboe’s research note says they tend to buy as the market rises and sell as the market falls in order to rebalance their hedge. That is the same direction as the move already underway, so the hedge can act like fuel on a fire. (cboe.com) When dealers are long gamma, the flow flips. Cboe says they hedge against the move by selling into rallies and buying into dips, which can damp volatility instead of amplifying it. (cboe.com) The effect gets stronger as expiration gets closer because short-dated options change sensitivity faster than longer-dated ones. The Options Clearing Corporation lists weekly options with roughly one to five weeks to expiration, and the fastest-moving corner of the market now includes zero-days-to-expiration contracts that expire the same day they trade. (theocc.com) (cboe.com) That same-day market is huge. Cboe said zero-days-to-expiration contracts made up 50% of Standard and Poor’s 500 Index option volume in August 2023, which is why traders watch dealer positioning so closely on volatile afternoons. (cboe.com) But “gamma did it” is not a universal answer for every selloff. In a 2024 note, Cboe said customer flow in zero-days-to-expiration Standard and Poor’s 500 Index options was still “extremely balanced,” leaving net market-maker gamma hedging at at most 0.2% of daily Standard and Poor’s 500 liquidity. (cboe.com) The useful read on a chaotic day is narrower than most headlines make it sound. A 3% intraday swing can be partly plumbing, partly macro news, and partly forced hedging, so the closing price may say less about long-term value than the speed of the move suggests. (cboe.com) (sifma.org)