Jamieson, Fausset & Brown, on Gen 6:4

“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.”

“giants--The term in Hebrew implies not so much the idea of great stature as of reckless ferocity, impious and daring characters, who spread devastation and carnage far and wide.”

Imported from an open dataset — not yet checked against the printed edition.