Basil of Caesarea

Strength of arm, swiftness of foot and comeliness of body—the spoils of sickness and the plunder of time—also awaken pride in man, unaware as he is that "All flesh is grass and all the glory of man as the flower of the field. The grass is withered and the flower is fallen." Such was the arrogance of the giants because of their strength. Such also was the God-defying pride of the witless Goliath.

HOMILY 20, Of Humility

Augustine of Hippo

All that we indubitably know, from the authentic Scripture in the Hebrew and Christian traditions, is the fact that in the period before the flood there were many giants, all of whom belonged to the earthly city in human society, and that there were sons of God descended from Seth who abandoned their holiness and sank down into this city of men. There is nothing surprising in the fact that giants could be born from men like that. …

City of God 15.23 ↗

Ambrose of Milan

But there were giants in the earth in those days. The author of divine Scripture does not want those giants to be regarded as the children of the earth in the manner of poets, but asserts that they were generated from angels and women, whom he calls with this name, desiring to express their bodily magnitude. …

On Noah and the Ark, Chapter IV ↗

Jerome

Now there were giants 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. For falling ones, or giants, Symmachus interpreted them as violent ones. And it is fitting for the name of falling ones to apply to angels and the children of the saints.

Hebrew Questions on Genesis ↗