Absalom met the servants of David, who, according to David's command, spared him, and gave him an opportunity to escape. His head caught hold of the oak; in which probably he was entangled by the hair of the head, which being very long and thick, might easily catch hold of a bough, especially when the great God directed it. Either he wore no helmet, or his helmet was such as left much of his hair visible; or he had thrown away his helmet as well as his other arms, to hasten his flight, or because of the heat of the season. Thus the matter of his pride was the instrument of his ruin, as also Asahel's swiftness, 2 Samuel 2:18, and Ahithophel's policy, 2 Samuel 17:23, were the occasions of their destruction. The mule that was under him went away; which might easily happen, because being in flight the mule passed along very swiftly.
Related Commentaries of 2 Samuel 18:9
2 Samuel 18:9
9 And Absalom met the servants of David. And Absalom rode upon a mule, and the mule went under the thick boughs of a great oak, and his head caught hold of the oak, and he was taken up between the heaven and the earth; and the mule that was under him went away.