Lee I contacted my broker interactive brokers regarding a short sell and be itm. I would think its the same with all brokers.
"When you short an option, you can be assigned at any time up to and including expiry date. Of course it is much more likely to happen when the option is in-the-money. However, assignment doesn't automatically happen just because the option is in-the-money. In your example, if VXX finishes below $15 on expiry day, your short $15 Put would be assigned."
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