In Genesis 6:4, the phrase “men of renown” uses the Hebrew word iysh. This term is used consistently as “man” or descendants of Adam—even Adam used it of himself in Genesis 2:23, yet it is never used of fallen angel, demons, or of Satan. It was used for some unfallen angels when they took the form of a man, though.
Never once have I found a verse in the Bible where wife, wives, husband, husbands, or marriage was anything other than between a human male and female. If these were marriages between fallen angels and women, then it opens up the possibility of marriages that are not limited to man and woman, when the Bible is clear on this subject.
Like the Sethite view, godly men (sons of God) were marrying women who were not godly (daughters of men), such as Cain’s (or others of Adam’s) descendants, including ungodly people from Seth’s line, thus resulting in Nephilim because they fell away from God’s favor. Once again, the Hebrew word Nephilim is related to the verb series “to fall.” For example, we know Cain fell away, and Lamech (descendant of Cain) and many other men and women had fallen away. The Nephilim could easily have been people who had fallen or turned from God in a severe way. This would also make sense as to why some of Canaan’s descendants (descendants of Anak were Canaanites) were called Nephilim in Numbers 13.
If you recall, Sodom and Gomorrah were so sinful that they were destroyed with direct intervention by God (Genesis 18:20, 19:24). This reminds me of the Flood—God Himself had a direct hand in destroying them (Genesis 6:13, 17). When Sodom and Gomorrah were destroyed, it is logical to assume that many descendants of those people who were not living in the area any longer were not destroyed. In fact, the Bible doesn’t say that all of the descendants of these places were completely destroyed. Therefore, it is logical that there could have been descendants living out away from the plain, such as Hebron, which is where the Anakites came from (Joshua 15:13).
The Bible indicates that the Anakites were descendants of the Nephilim, but it couldn’t have been those wiped out in the Flood, since God destroyed all land flesh. Therefore, it had to be group a people that were post-Flood. If the Nephilim had fallen so far pre-Flood that God Himself destroyed the earth as a result of their sin, then it makes sense that the post-Flood account of similar but smaller scale destruction in Sodom and Gomorrah may well have been the Nephilim. With the Anakites, who were Canaanites like those in Sodom and Gomorrah, they may very well have been their descendants.
It makes more sense that they were relatives/descendants from Sodom and Gomorrah (and the other cities of the plain). The sinners who died in the Flood and the sinners in Sodom and Gomorrah had one significant thing in common—they were the ones in history to fall so far from God that God Himself had a direct hand in destroying them. So, it makes sense why these two groups could both be called Nephilim in this view: 100% human descendants of Adam who were in a state of being fallen far from God. Of course, there should be no dogmatism about this point.
— Answers in Genesis, Who Were the Nephilim