Rashi, Da'as Zekenim and Rosh: Because they too, like Gad, ¹ dwelled on the border (and guarded Yisrael from their enemies).

Rashi #1 (citing Targum Onkelos) and Targum Yonasan: It refers to the River Yarden, which originates from the Bashan, and flows from the Banyas Cave, otherwise known as 'Leshem', which is situated in the portion of Dan. ¹

Rashi #2: Just as 'Zinuk' refers to a river that flows from one location but splits into two, so too, is the tribe of Dan destined to receive their portion in two places - first in the north-west, in Ekron and its environs, and later they fought and captured Leshem, ² in the north-east of the country, which is synonymous with Banyas, from which the Yarden flows.

Rashi #3 (in the explanation on the prayer for rain of R. Elazar ha'Kalir ascribed to him): It refers to the River Yarden, which flows from the mountain of Bashan in the rain season, causing the grass and the vegetaion to grow - for the consumpton of the calves.

Seforno: It means that Dan will spring from the Bashan, a choice area for grazing sheep and cattle ³ - and from where a lion will not spring, unless it knows for sure that it will catch its prey; so too, will Dan be sure that, when they attack, they will destroy the enemy.

Da'as Zekenim and Rosh: It refers to the Yarden, which separates between Bashan (Og's territory, which Gad received) and Dan (which is west of the Yarden). "Lot chose the plains of the Yarden because it was well-watered". ⁴

Oznayim la'Torah: After receiving their portion in the middle of the country, ⁵ Dan captured Leshem on the north-eastern tip - north of the Kineret, which meant that they actually inherited land east of the Yarden together with half the tribe of Menasheh in the territory of Og Melech ha'Bashan, ⁶ thereby assisting Menasheh to guard the north of the country against invading armies.