Mosiah 11:16

And it came to pass that the Lamanites began to come in upon his people, upon small numbers, and to slay them in their fields, and while they were tending their flocks.

The Lamanites began attacking his people in small groups. They killed them in their fields and while they were taking care of their animals.

The Lamanites started attacking in small groups—killing people in the fields and while they were tending their flocks.