In his abridgment of Alma's record, Mormon, in many places, interpolated comments intended to explain certain historical data, thereby throwing light upon what otherwise might be difficult narrations. In this verse, Mormon does just that. He tells us that it was a custom among the Lamanites, who we already know were a thieving and a plundering lot, to steal the cattle of the people who gathered them at the Waters of Sebus. To Mormon's comment we may add one of our own: that by a ruse the would-be-robbers stampeded the flocks and herds that had trekked there, perhaps for miles, to obtain water to drink. By their shouts and prolonged yelling, the rustlers scattered the frightened beasts in all directions, then the robbers would seek to drive them away to their own lands.
The modern method of branding livestock to mark legal title was evidently not practiced at that time, and real ownership of on-the-hoof animals was not easily established. At any rate, the owners of such cattle thought it was cheaper and at least less burdensome to hold the herdsmen responsible for their safety than for them to seek out and punish the thieves.