The call and put walls are the strikes with the heaviest options open interest above and below price. Because dealers hedge that open interest, those strikes act like the day's rails — levels price is drawn toward, stalls at, and often refuses to leave. Knowing how to read behavior at a wall is where the concept turns into something usable.
At the call wall
The call wall usually sits above price and behaves like a ceiling. In a positive-gamma regime, dealer hedging leans against advances into it — price tends to grind up, stall, and pin near the wall rather than blow through. That makes the call wall a natural target zone for a move up, and a spot to expect resistance rather than continuation.
At the put wall
The put wall sits below and behaves like a floor. The same hedging that caps rallies at the call wall tends to cushion declines at the put wall — dips get absorbed, and price often bounces from the level. It's the downside bookend of the day's likely range.
When a wall holds — and when it breaks
The regime decides the rules. In positive gamma, walls hold: dealers dampen moves, so pins and reversals at the walls are the base case. In negative gamma, walls become launchpads: dealer hedging amplifies moves, so a break of a wall can accelerate rather than reverse. The same level means opposite things depending on which side of the gamma flip you're on.
A wall isn't a wall in every weather. In positive gamma it repels; in negative gamma, once broken, it can pull price faster the other way.
The magnet effect into expiration
As expiration approaches, large open-interest strikes exert a stronger pull — the “pin” you sometimes see into a Friday close. The nearer the expiry and the bigger the strike, the more price tends to gravitate toward it, all else equal.
Using the walls
Treat the walls as structure, not signals. They mark where a move is likely to stall or find support, where a target is realistic, and where a break would mean something. Combined with the regime and the expected move, they become the level layer of the full dealer-positioning read — the terrain, not the trade.