Adam Clarke on Deuteronomy 33:22

Dan is a lion's whelp: he shall leap from Bashan - The Jewish interpreters observe that Bashan was a place much frequented by lions, who issued thence into all parts to look for prey. By this probably Moses intended to point out the strength and prowess of this tribe, that it should extend its territories, and live a sort of predatory life. It appears from Jos 19:47, that the portion originally assigned to this tribe was not sufficient for them; hence we find them going out to war against Leshem and taking it, adding it to their territories, and calling it by the name of the tribe. Jacob, in his prophetic blessing of this tribe, represents it under the notion of a serpent in the path, Gen 49:17. The character there, and that given here, constitute the complete warrior-stratagem and courage. See the note on Gen 49:17.