‘ And Joshua said, “Roll large stones over the mouth of the cave, and set men by it so as to retain them. But do not yourselves stay, pursue after your enemies and smite those who are at the rear. Do not allow them to enter into their cities. For Yahweh your God has delivered them into your hand.” '
Joshua's instructions were that while the kings should be held securely by trapping them in the cave the pursuit must go on. As many as possible of the armies must be killed, for there would then be less of a threat in the future. We are probably to see that the five kings had their bodyguards with them otherwise they could have been retained and bound. So they were not to waste time making the final capture but to concentrate on maximum effectiveness. The trapped kings and their bodyguards could be dealt with later. No doubt some local had been made to reveal whether there was any other way out of the caves.