Mosiah 21:19

and the king himself did not trust his person without the walls of the city, unless he took his guards with him, fearing that he might by some means fall into the hands of the Lamanites.

The king himself didn’t go outside the city walls without his guards. He was afraid he might somehow be caught by the Lamanites.

The king himself wouldn’t go outside the city walls without his guards, afraid he might somehow fall into Lamanite hands.