Spears and similar weapons are well suited to fighting in deep formations. Weapons used for fighting in ranks enable troops in a second or subsequent rank to fight in close combat as well as the warriors in the first rank who are actually touching the enemy. For example, a unit of Spearmen can fight in two ranks - warriors in the second rank can stab past their comrades using their long spears.
If a unit is entitled to fight in this way then any model in a second or subsequent rank can fight if it is behind a model that is engaged in close combat to its front. Extra ranks cannot fight to their side or rear but only to their front. Where a weapon can fight in two or more ranks, this is indicated in the weapon's description, for example, 'spears fight in two ranks'.
In order to employ all of its additional ranks as described, a unit must not have moved in that turn. If a unit has moved, if it has charged for example, then it fights with one less rank than it otherwise would. For example, a unit of Spearmen can normally fight in two ranks, but will fight with only the front rank if they charge. The unit will be able to fight with the extra rank during subsequent rounds of close combat.