‘For Joshua did not draw back his hand back with which he stretched out his spear, until he had utterly destroyed all the inhabitants of Ai.'
It would appear that having stretched out his spear as a signal he then continued to hold it out as a gesture of victory, until the victory was complete (compare the rod of Moses in Exodus 7:29; Exodus 8:16 and the hands of Moses in Exodus 17:12). In a sense it was the spear of YHWH. It was the sign that YHWH fought for them.