English Explanation of Mishnah Sanhedrin 7:9

He who has sexual relations with a betrothed young woman is not punished until she is a young woman, a virgin, betrothed, and in her father's house.
If two men had sexual relations with her, the first is stoned, but the second is strangled.
Mishnah nine deals with a man who has relations with a betrothed virgin.
Deuteronomy 22:23-24 states: “In the case of a virgin who is betrothed to a man if a man comes upon her in town and lies with her, you shall take the two of them out to the gate of that town and stone them.” A man who has sexual relations with a betrothed woman is an adulterer, as is she, and they are both punishable by death. However, unlike a regular adulterer who is punished by strangulation, one who has relations with a betrothed woman is punished with a more serious form of the death penalty, stoning. Our mishnah teaches that in order for the two to be punished by stoning she must be betrothed and not married. She must be a virgin, and she must be a young woman, usually defined as being from the age of 12-12 ½. Older or younger than that and he will only be punished by strangulation. She also must still be residing in her father’s house. If she has already moved to her husband’s house she is considered married and adultery is then punished by strangulation.
If two men commit adultery with her the first is punished by being stoned and the second is punished by strangulation, since by the time he had relations with her she was no longer a virgin.