Units have the ability to block to parry attacks, their chance to do so will depend on their level and the level of the attacker, also the type of unit/attack/weapon the attacker is using as well as the type of unit/weapon the defender is using. For example, an archer is going to be hard pressed to block or parry an attack from a cutting or stabbing weapon with a wooden bow.
There will possibly be other attacks and defenses units will learn at higher levels such as berserking, ripostes, and better combinations.
Continuing on with our theme of "realistic fantasy" we are trying to get away from the whole cut and dry math of RTS where Warrior does 8 damage, or even Warrior does 8HP damage or 6AP damage. There are a lot of variables that go into combat in DoF.