Alma 43:36 - 43:40
Alma 43: 36 And it came to pass that the Lamanites, when they saw the Nephites coming upon them in their rear, turned them about and began to contend with the army of Lehi.
When the Lamanites saw that they were beginning attached from their rear, they turned to contend with the army of Lehi.
Alma 43: 37 And the work of death commenced on both sides, but it was more dreadful on the part of the Lamanites, for their nakedness was exposed to the heavy blows of the Nephites with their swords and their cimeters, which brought death almost at every stroke.
As the battle began, the Lamanites were taking the greater losses because of their lack of body protection. Their nakedness left them open to the sword strikes of the well protected Nephites.
Alma 43: 38 While on the other hand, there was now and then a man fell among the Nephites, by their swords and the loss of blood, they being shielded from the more vital parts of the body, or the more vital parts of the body being shielded from the strokes of the Lamanites, by their breastplates, and their armshields, and their head-plates; and thus the Nephites did carry on the work of death among the Lamanites.
The result was the Lamanites were being killed at almost every stroke of the Nephites swords, while a Nephites would fall now and then. Because of their body protection, the Lamanites could not inflicted any wounds or fatal blows in any large numbers on the Nephites. With that advantage, the army of Lehi, was killing the Lamanites in great numbers.
Alma 43: 39 And it came to pass that the Lamanites became frightened, because of the great destruction among them, even until they began to flee towards the river Sidon.
The Lamanites could now see they would be completely destroyed if they stayed and fought, so they began to flee across the river to escape Lehi’s army.
Alma 43: 40 And they were pursued by Lehi and his men; and they were driven by Lehi into the waters of Sidon, and they crossed the waters of Sidon. And Lehi retained his armies upon the bank of the river Sidon that they should not cross.
Lehi presumed them but when the Lamanites entered the waters of the river Sidon, they stopped on the shore to make sure they did not return to the bank of the river.