His mischief - The mischief which he had designed for others.
Shall return upon his own head - Shall come upon himself. The blow which he aimed at others shall recoil on himself. This is but stating in another form the sentiment which had been expressed in the two previous verses. The language used here has something of a proverbial cast, and perhaps was common in the time of the writer to express this idea.
And his violent dealing - Which he shows to others. The word rendered violent dealing means violence, injustice, oppression, wrong.
Shall all come down upon his own pate - The word here rendered "pate" means properly vertex, top, or crown - as of the head. The idea is that it would come upon himself. He would be treated as he had designed to treat others. The sentiment here expressed is found also in Psalm 9:15; Psalm 35:8; Psalm 37:15. Compare Eurip. Med. 409, and Lucretius v. 1151.

Shall come down upon his own pate - Upon his scalp, קדקד kodkod, the top of the head. It may refer to knocking the criminal on the head, in order to deprive him of life. Had scalping been known in those days, I should have thought the reference might be to that barbarous custom.

His mischief shall return upon his own head,.... That which he conceived and devised in his mind, and attempted to bring upon others, shall fall upon himself, as a just judgment from heaven upon him;
and his violent dealing shall come down upon his own pate; referring to the violence with which Saul pursued David, which would be requited to him, and of which he prophesied, 1-Samuel 26:10.