Call resistance & put support

Where the gamma actually sits

Call Wall and Put Support: Why Price Reacts at Heavy Strikes — 53 seconds, on a real session. Watch on YouTube

Dealer gamma is not spread evenly across strikes — it piles up where the open interest is. The strike carrying the largest concentration above spot is commonly called the call wall (this site labels it call resistance, CR); the heaviest concentration below spot is the put support (PS).

Why price reacts there

Near a heavy strike, dealer hedging intensifies. Approaching a call wall in a long-gamma regime, every further point up forces more dealer selling — rallies run into a mechanical headwind, which is why price so often stalls, consolidates, or pins near the wall into expiry. Put support works as the mirror image on the way down. Neither is a hard floor or ceiling: on a strong enough move, or once heavy strikes roll off at expiry, the level simply migrates.

0DTE makes the walls move

With most SPX volume now in same-day options, the walls are not static daily levels — they build and dissolve intraday as flows arrive. That is why FirmTape recomputes them continuously from the tape rather than once per morning: the CR and PS lines on the terminal move as the positions behind them move. Where the walls sit right now, free and fifteen minutes behind, is on /now. The expected-hold band on each session page shows the range those concentrations implied, and the session summary records whether the day respected it; the archive-wide tally is in level hold rates.

Related reading: what GEX measures and the zero-gamma flip.