The herbivores stampeded toward the ranks. They aren't chasing the tribes but are herded by the wolves behind them. The beasts have fear in their eyes. It's a fear only an herbivore can muster. They hurled themselves at the volley of arrows and trampled on their own dead.
Tribesmen ride their horses and shoot their arrows. There are several kilometers until they reach the chokepoints that are set up. In order to fend off the stampeding herbivores, they lose some ground as they try to maintain an effective range. The ground the tribesmen claimed as their territory is a war resource. Every bit of ground lost to the beasts is a loss. But it's better to lose some ground than lose the lives of the tribesmen.
