Etymology of "Grasson"

Grasson appears to be derived front "grassor," "to assail." Livy somewhere has the following—"Grassor in possessionem agri" —which would be rendered, "To enter upon it by force;" it being only by the payment of the fine (Grasson) that the entry, "Grassor," or alienation of copyhold lands, could be warded off: hence the act of the lord of the manor (Grassor) became the name for the fine paid by this tenant, "Grasson."