3 Nephi 4:24

And now Gidgiddoni, being aware of their design, and knowing of their weakness because of the want of food, and the great slaughter which had been made among them, therefore he did send out his armies in the night-time, and did cut off the way of their retreat, and did place his armies in the way of their retreat;

Gidgiddoni knew their plan. He knew they were weak from lack of food. He knew many of them had been killed. So he sent his armies out at night. They blocked the way the robbers would run. They got in the way of their escape.

But Gidgiddoni knew what they were planning. He understood how weak they’d become from starvation and massive losses. So he sent his armies out at night and blocked their escape route.