It is important for Helaman to note that the went a “considerable distance.” Had they been very close to Antiparah, the logical thing to do would be to attempt a return to Antiparah where they would not only be accepted into the city, but where reinforcements could come to help turn the tide of the battle. Being far from Antiparah guaranteed that his army of Lamanites was cut off, a fact that they quick recognized.
Even though they have been trapped by a stratagem, we need not suppose that they did not understand the stratagem when it was sprung against them. They understood that the trailing army would probably be bigger than the one they were chasing, and the smaller army ahead of them was intended to turn and harass their rear when they turned to meet the arriving troops. Rather than allow the strategy to unfold as planned, they pushed forward their attack on Helaman’s men to overtake and destroy them. If they accomplished that task, they could then turn to the pursuing Antipus and meet him on a more level strategic position, without the immediate worry of a two-front battle.