Exact Formula:
Unit has equipment that has attack values that gives the unit an overall attack rating.
Every type of equipment has an attack type: Normal, Cutting, Blunt, Piercing.
Whichever type of non-normal attack contributes the most to your attack rating defines your overall attack type. (Realistically, your primary weapon).
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Unit has equipment that has defense values that gives the unit an overall defense rating.
Every type of equipment has a defense against certain types of attack. Whatever contributes the most to your overall defense results in your unit's overall defense type.
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In combat:
Attacker rolls a value 0 to attack max value.
Defender rolls a value 0 to defense max value.
If Defender defense type = Attacker's attack type then defender's roll = max value.
Thus, a player armed with a club (blunt damage) with an attack of 5 goes up against a guy with a helmet (protection from blunt) of defense of 3 then the defender will always roll a 3 against the attacker. They'll still take 2 damage potentially but they'll be a lot safer.
By contrast, no helmet but instead has Leather armor with a defense value of 4, they'll be rolling 0 to 4 against that club.
Some equipment has defensive values that allow a dodge % (shields) that have a chance that a player will simply avoid certain types of attack but that's a different discussion.
It's important to remember this: IT IS NOT A ROLE PLAYING GAME. We have to, between turns, simulate potentially hundreds of battles so we can't have D&D level complexity in individual battles but we can get a pretty good approximation.
