Genesis 6:4

הנפילים THE GIANTS — Thy were called נפילים because they fell (נפלו) and caused the downfall of (הפילו) the world (Genesis Rabbah 26:7). In Hebrew the giants are usually called בימים ההם .ענקים IN THOSE DAYS — In the days of the generations of Enosh and the sons of Cain (Genesis Rabbah 26:7). וגם אחרי כן AND ALSO AFTER THAT — Although they witnessed the destruction of the generation of Enosh when the Ocean rose and flooded a third part of the world, yet the generation of the Flood did not humble itself and take a lesson from them (Genesis Rabbah 26). אשר יבאו WHEN [THE SONS OF GOD] CAME IN, they (the women) bore children, giants like them (the fathers) (Genesis Rabbah 26:7). הגבורים MIGHTY — in rebellion against God. אנשי שם MEN OF RENOWN (literally, men of name) — Men who bore distinctive names: עירד, מחויאל, מתושאל being so named because these names have reference to their destruction, for they were wiped out and torn out from the world (מחוי-אל would signify “wiped-out-by-God”, מתושאל “Torn-out-by-God). Another explanation is that they were men of devastation (אנשי שם-מון) — who devastated the world (Genesis Rabbah 26:7).

הַנְּפִלִ֞ים הָי֣וּ בָאָ֘רֶץ֮ בַּיָּמִ֣ים הָהֵם֒ וְגַ֣ם אַֽחֲרֵי־כֵ֗ן אֲשֶׁ֨ר יָבֹ֜אוּ בְּנֵ֤י הָֽאֱלֹהִים֙ אֶל־בְּנ֣וֹת הָֽאָדָ֔ם וְיָלְד֖וּ לָהֶ֑ם הֵ֧מָּה הַגִּבֹּרִ֛ים אֲשֶׁ֥ר מֵעוֹלָ֖ם אַנְשֵׁ֥י הַשֵּֽׁם׃ {פ}

There were Nefilim in the earth in those days; and also after that, when the distinguished men came in to the daughters of men, and they bore children to them; the same were mighty men of old, men of renown.