Alma 18:7

Now it was the practice of the Lamanites, to stand by the waters of Sebus, to scatter the flocks of the people, that thereby they might drive away many that were scattered, unto their own land, it being a practice of plunder among them.

The Lamanites had a practice of standing by the waters of Sebus to scatter the people’s flocks. That way they could steal many that were scattered and drive them away to their own land. Stealing was a practice among them.

This was a common Lamanite tactic: hang around the waters of Sebus, scatter people's flocks, then drive the scattered animals back to their own territory. It was basically organized theft.