Obstacle penalty
From The Heroes of Might and Magic III wiki
Obstacle penalty is a term for reduction of damage for ranged attacks. It occurs only during sieges when the target is behind walls. Attack suffering from obstacle penalty only does half the damage compared to attack made target being in front of the wall. Obstacle penalty is cumulative with the range penalty.
Sharpshooters, Enchanters and Arch Magi ignore the obstacle penalty, as do all creatures under a command of a hero with either the Golden Bow or Bow of the Sharpshooter combination artifact equipped.
Obstacle penalty is undone once drawbridge or all destroyable fortification elements (siege walls, drawbridge, arrow towers) are breached (validate!).
