Assignment

権利割当。買い手が権利行使したため、売り手が契約の履行（株式の受け渡しや買い付け）を求められること。

Assignment is what happens to an option seller when the buyer decides to exercise. If you sold a call, you get assigned and must deliver 100 shares per contract at the strike; if you sold a put, you get assigned and must buy 100 shares at the strike. It is the flip side of exercise: the buyer chooses, and as the seller you have no say once it happens.

In practice, most traders meet assignment through short options that drift in the money. A cash-secured put is the classic case: you sell a put on a stock you would happily own, collect the premium, and if the stock falls below the strike you may be assigned and end up buying the shares at that price. That is often the plan, not an accident.

The common mistake is forgetting that American-style options can be assigned early, especially short calls the day before an ex-dividend date, or deep in the money legs of a spread. If only one leg gets assigned, you can suddenly hold a large stock position overnight. Watch in the money short options as expiration nears and close or roll them before assignment forces your hand.

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