Pin Risk

Pin risk is the uncertainty that comes from an option expiring with the stock price sitting almost exactly at the strike price. "Pinned" refers to the stock appearing stuck right at that strike as expiration approaches, like it's pinned to that number on the chart.

The problem shows up because assignment on options is based on whether the option is in-the-money at expiration, and that determination happens after trading has already closed for the day. If a stock closes at $50.01 and you sold a $50 call, that option is technically in-the-money by a penny and will likely be exercised, meaning you now owe 100 shares per contract to the buyer. If it closes at $49.99 instead, the same call expires worthless and you owe nothing. The seller has to decide how to hedge or manage their position before knowing which outcome actually happened, because the closing price isn't final until after the market shuts.

The nuance that trips people up is that pin risk isn't really about the option's price moving, it's about a binary, all-or-nothing outcome around assignment that gets decided by a razor-thin difference in the underlying stock. Someone holding what they think is a fully hedged position (long the stock to offset a short call, for example) can wake up Monday holding either a full stock position, no stock position, or something in between, depending on whether their contracts got assigned. Some holders also don't realize that even out-of-the-money options can occasionally be exercised for reasons unrelated to price, adding another layer of unpredictability.

Pin risk mainly matters right around expiration, typically in the final trading session and overnight before contracts settle. It fades once the stock moves clearly away from the strike, since a $52 close against a $50 strike leaves no doubt about the outcome.