Velliscig wrote:But why stand there and wait to be shot!? Why not run away and call up cavalry or something. Confusing.
Because the moment you turn to run away the battle is lost and you are either dead or dropping all your armour and weapons and loot to run faster.
See, usually the other side has cavalry as well. The point of artillery (archers) is to break up infantry formations (aka cannon fodder) so cavalry (knights and men-at-arms on horseback) can ride individuals down and kill or capture them. A body of armed and trained men that stands its ground is not vulnerable to horses unless gaps can be created in the formations by maneuver or attack from artillery.
When facing archers you can try to wait them out with if they have a short supply of arrows and/or you have enough cover (shields/terrain) or you can attack them with your own cavalry (fast moving=good) or infantry (slow moving=bad).
But in any case, to win the battle you have engage the enemy. Armoured infantry cannot retreat in good order any faster than archers can advance so your suggestion they they "run away" is not possible as if you back up slowly they simply follow and keep shooting. If you actually run at speed you have lost the battle and the best you can hope is to rally your troops far enough away that your enemies will not have followed.