I quote five translations whose returns, in my opinion, have changed the text and therefore the meaning of Genesis 6:4.
New Living Translation
In those days, and for some time after, giant Nephilites lived on the earth, for whenever the sons of God had intercourse with women, they gave birth to children who became the heroes and famous warriors of ancient times.
International Standard Version
The Nephilim were on the earth at that time (and also immediately afterward), when those divine beings were having sexual relations with those human women, who gave birth to children for them. These children became the heroes and legendary figures of ancient times.
Now giants were upon the earth in those days. For after the sons of God went in to the daughters of men and they brought forth children, these are the mighty men of old, men of renown.
Good News Translation
In those days, and even later, there were giants on the earth who were descendants of human women and the heavenly beings. They were the great heroes and famous men of long ago.
NEW WORLD TRANSLATION OF THE HOLY SCRIPTURES (2013 REVISION)
The Neph′i·lim* were on the earth in those days and afterward. During that time the sons of the true God continued to have relations with the daughters of men, and these bore sons to them. They were the mighty ones of old times, the men of fame.
The concept of the verse, as it appears in these translations are similar. Connecting the Nephilim as the offspring of the fallen angels. Other translations may think the same, but leave the text intact.
(the hermeneutics performance belongs to John T. Kolitsara
Verse 4. – There were. Not became, or arose, as if the giants were the fruit of the previously-mentioned misalliances; but already existedcontemporaneously with the sons of God (cf. Keil, Havernick, and Lange).Giants. Nephilim, from naphal, to fall; hence supposed to describe the offspring of the daughters of men and the fallen angels (Hoffman, Delitzsch). The LXX, translate by γίγαντες; whence the “giants” of the A.V. and Vulgate, which Luther rejects as fabulous; but Kalisch, on the strength of Numbers 13:33, accepts as the certain import of the term. More probable is the interpretation which understands them as men of violence, roving, lawless gallants, “who fall on others;” robbers, or tyrants (Aquila, Rosenmüller, Gesenius, Luther, Calvin, Kurtz, Keil,. Murphy, ‘Speaker’s Commentary’). That they were “monsters, prodigies” (Tueh, Knobel), may be rejected, though it is not unlikely they were men of large physical stature, like the Anakim, Rephaim, and others (cf. Numbers 13:33). In the earth. Not merely on it, but largely occupying the populated region. In those days.
Gill’s Exposition of the Entire Bible
There were giants in the earth in those days,…. That is, in the days before the sons of God took the daughters of men for wives, in such a general manner as before declared, or before the declension and apostasy became so universal; even in the times of Jared, as the Arabic writers (n) understand it, who say that these giants were begotten on the daughters of Cain by the children of Seth, who went down from the mountain to them in the days of Jared, see Genesis 5:20 the word “Nephilim” comes from a word which signifies to fall; and these might be so called, either because they made their fear to fall upon men, or men, through fear, to fall before them, because of their height and strength; or rather because they fell and rushed on men with great violence, and oppressed them in a cruel and tyrannical manner; or, as some think, because they fell off and were apostates from the true religion, which is much better than to understand them of apostate angels, whom the Targum of Jonathan mentions by name, and calls them Schanchazai and Uziel, who fell from heaven, and were in the earth in those days:
and also after that, which shows that the preceding clause respects giants in former times:
when the sons of God came in unto the daughters of men, came into their houses and chambers, and lay with them:
and they bare children unto them, or giants unto them, as may be supplied from the former clause; for the sense is, as there were giants before this general defection, so there were at this time, when there was a mixture of the Cainites and Sethites; which were the offspring of the sons of God, or posterity of Seth, mixing with the daughters of men, or the posterity of Cain; for this is not to be understood after the flood, as Aben Ezra, Ben Melech; and so they are described in the following words:
the same became mighty men; for tallness and strength, for power and dominion, for tyranny and oppression:
4. The Nephilim] i.e. giants. It is natural to refer to Numbers 13:33, “And there we saw the Nephilim (Or, giants), the sons of Anak, which come of the Nephilim; and we were in our own sight as grasshoppers, and so we were in their sight.” The tradition that the Nephilim existed at the time of the Exodus was therefore quite strongly held. The precise meaning of the name has been lost. The passage in Numbers shews clearly that it denoted men of gigantic stature. The etymology very probably goes back to primitive times; and its origin is lost with the dialects that disappeared when the Israelites finally occupied Palestine. It was natural to connect the word with the Hebrew naphal, “to fall”; hence arose the renderings of Aquila, οἱ ἐπιπίπτοντες, “the assailants,” and of Symmachus, οἱ βιαῖοι, “the violent,” while among Patristic commentators the word was connected with “the fallen angels.” But these are merely guesses; and we must be content to leave the etymology of “the Nephilim,” like that of “the Rephaim” and “the Anakim,” unexplained.
and also after that] These words are introduced very awkwardly; and were very probably added as a gloss, in order to shew that the Nephilim existed not only in primitive ages, but also at the time of the Exodus from Egypt, as would be implied by Numbers 13:33. The continuance of the Nephilim in later times seems to contradict the account of the destruction of all the dwellers on the earth by the Flood. This contradiction is to be explained on the supposition, mentioned above, that the present passage is a fragment of a tradition in which the Flood was not recorded.
the mighty men, &c.] That is to say, “the well-known giants of old-world time,” familiar personages in Israelite folk-lore. To this class belong such names as “Nimrod,” Genesis 10:8, and “Og,” Deuteronomy 3:11.
Two classes of men, with strong hand and strong will, are here described. “The giants,” the well-known men of great stature, physical force, and violent will, who were enabled by these qualities to claim and secure the supremacy over their fellow-men. “Had been in the land in those days.” In the days when those intermarriages were beginning to take place, the warriors were asserting the claim of might. Violence and rapine were becoming rampant in the land. “And after that.” The progeny of the mixed marriages were the second and subsequent class of leading men. “The sons of God” are here contradistinguished from the “nephilim, or giants,” who appear therefore to have belonged to the Cainites. The offspring of these unhallowed unions were the heroes, the gallants, the mighty men, the men of renown. They were probably more refined in manners and exalted in thought than their predecessors of pure Cainite descent. “Men of name,” whose names are often in men’s mouths, because they either deserved or required to be named frequently on account of their influential or representative character. Being distinguished from the common herd by prominent qualities or memorable exploits, they were also frequently marked out by a special name or surname, derived from such trait of character or deed of notoriety. “Of old” (מעולם mē’ôlām). This has been sometimes explained “of the world,” in the sense of αἰών aiōn; but the meaning is too late for the present passage. The phrase uniformly means “of old,” covering a more or less extensive length of time. This note of time implies a writer probably after the deluge, who could speak of antediluvian affairs, as happening of old.
The Greek Septuagint also suggests that both the “Nephilim” and “mighty ones” are identical by using the same word gi′gan·tes (giants) to translate both expressions.
Reviewing the account, we see that verses 1 to 3 tell of “the sons of the true God” taking wives and of Jehovah’s statement that he was going to end his patience with men after 120 years. Verse 4 then speaks of the Nephilim proving to be in the earth “in those days,” evidently the days when Jehovah made the statement. Then it shows that this situation continued “after that, when the sons of the true God continued to have relations with the daughters of men,” and describes in more detail the results of the union of “the sons of the true God” with women.
HEB: הַנְּפִלִ֞ים הָי֣וּ בָאָרֶץ֮
NAS: The Nephilim were on the earth
KJV: There were giants in the earth
INT: the Nephilim were on the earth