TSK
Treasury of Scripture Knowledge references in NET.
The Nephilim were on the earth in those days(and also after this) when the sons of God would sleep with the daughters of humankind, who gave birth to their children. They were the mighty heroes of old, the famous men.
He slept with Hagar, and she became pregnant. Once Hagar realized she was pregnant, she despised Sarai.
Then Judah said to Onan,“Sleep with your brother’s wife and fulfill the duty of a brother-in-law to her so that you may raise up a descendant for your brother.”
Respect for the Sanctity of Others If brothers live together and one of them dies without having a son, the dead man’s wife must not remarry someone outside the family. Instead, her late husband’s brother must go to her, marry her, and perform the duty of a brother-in-law.
(For they were afraid, and he did not know what to say.)