Every time a unit is attacked or prevents an opponent from attacking through repelling, it gets a point of harassment penalty. Each point of harassment penalty reduces the unit’s defense by 1. The penalty is multiplied by 95/100 every 320 ticks (or 23.4375 times a round)¹⁾, so the penalty goes down quickly if it is high and the unit is no longer being attacked.

A weapon with multiple attacks inflicts 1 point of harassment penalty for each one of its multiple attacks.

Mounted units are only half as affected, requiring two attacks to suffer one point of harassment penalty. A mounted unit completely surrounded by 3-per-square, 1-attack-per-turn units bottoms out at -10 defence harassment penalty. Note that harassment penalties from successfully repelling are not halved.

A unit with Unsurroundable will receive a reduced harassment penalty from being attacked multiple times in a round. Eg. Unsurroundable(3) means a unit can be attacked 3 times before receiving any harassment penalty.

Harassment replaces Multiple Attack Penalty in previous iterations of Dominions