Table of contents
Start with coordinates
An option surface is easier to reason about after separating three coordinates: expiry, moneyness, and implied volatility. During a selloff, each can move at once. A chart that holds strike fixed may therefore tell a different story from one that holds delta fixed.
For a first pass, I compare implied volatility by delta and days to expiry. This keeps the question narrow: how did the market reprice similarly exposed options as spot fell?
The recurring pattern
In a stylized equity drawdown, short-dated volatility rises fastest and downside skew steepens. The front of the surface reflects immediate demand for protection; the left tail reflects the asymmetric value of that protection.
One compact diagnostic is the 25-delta risk reversal,
For equities it is often negative, and it commonly becomes more negative under stress. That observation is descriptive. It does not, by itself, identify who traded, why they traded, or whether the move predicts the next return.
What the picture cannot establish
Surfaces are model-dependent summaries. Sparse quotes, changing rates, dividends, wide spreads, and stale marks all matter. A clean visual can hide messy inputs.
I therefore treat the surface as a map of prices, not a direct map of beliefs. The excursion becomes useful when it produces sharper questions: Which maturities moved first? Did skew change after controlling for spot? How large was the move relative to bid–ask width?
Takeaway
The most interesting feature of a selloff is rarely that “volatility went up.” It is how the shape changed. Term structure locates urgency in time; skew locates it across states of the world.