Pin risk occurs when an underlying stock’s price closes near the strike price of an options contract on expiration day, leaving traders uncertain whether their options will expire in the money (ITM) or out-of-the-money (OTM). This uncertainty creates risk for options writers (sellers), who may face unexpected assignments if the stock price "pins" at the strike price.

Connection to the Witching Hour
The witching hour—the final hour of trading on triple witching days (when stock options, index options, and futures expire)—often sees heightened volatility as traders adjust or close positions. During this time:

Market makers hedge exposures, increasing price swings near key strike prices.

Large institutional trades can push stocks toward popular strike prices, increasing pin risk.

Last-minute exercises of near-ATM options create unpredictable assignments for sellers.

Traders managing multi-leg strategies (like spreads) face amplified pin risk if underlying stocks hover around strike prices at expiration. To mitigate this, many close positions before the witching hour or monitor order flow for signs of price "pinning."

In summary, pin risk is a key concern during the witching hour due to expiration-driven volatility and the potential for unexpected obligations in options contracts.