Pin risk

ピン・リスク。満期に株価が売り建てた権利行使価格ちょうどで引けたときの不確実性で、割り当てられるか否かが読めず、想定外のポジションが残る恐れがある。

Pin risk is the uncertainty a trader faces when an option finishes right at its strike as expiration approaches. If the underlying closes almost exactly on the strike, you genuinely don't know whether the option will be exercised or expire worthless, and that leaves you unsure whether you'll be assigned stock over the weekend.

Say you're short a 50 call and the stock settles at 50.02 on expiration Friday. It might be exercised, might not. If you hedge assuming assignment and buy stock to stay flat, but the call is never exercised, you walk into Monday holding an unwanted position that gaps against you. That surprise directional exposure is the real cost of pin risk.

The common mistake is assuming that anything even slightly in the money is automatically exercised. Contra-exercise and after-hours moves happen, so options exactly at the money are the danger zone. Traders manage this by closing positions before the close on expiration day rather than gambling on where the pin lands.

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