Sure, I can pick up a stick and hit you with it. No formal training. If you let me. If I try and take a swing at you, you could block, parry, or dodge. But which one will you do? If you are fighting a sword and board npc, they can effectively do one of the three (just because you have shield doesn't mean you can't use your weapon to stop an attack). So already, you have room here for a chance of occurrence. It could be set up based on your weapon skill vs their block, parry, and dodge skills. Now, the game doesn't have a skill for parry and dodge so there is something that could be added.
The equation itself would be a bit complex since it would have to work with the full range of 1 to 100 in each skill involved but basically at the top end (all skills being 100) it would leave you with a 50% chance to hit. With regards to the the 50% chance to miss, it could be broken down into 25% chance to block, a 15% chance to parry and a 10% chance to dodge. If the npc were to have a second weapon instead of a shield, then you end up with a 40% to miss (15% x 2 + 10%). The npc traded off defense for more offense. If they went with a 2H, then you now have 25% to miss. Which would mean that the damage of weapons would have to be such that a 2H > two 1H's. Armor can then have an effect on things like dodge. If you are wearing no armor, you get the full benefit from dodge but if you were to start equipping light armor pieces, the effectiveness of your dodge would go down (perhaps down by 20% when fully equipped resulting in a 8% instead of 10%). Then if you put on heavy, it would drop by as much as another 20% for a maximum drop of 40% when equipped in all heavy armor (so your dodge is 6% instead of 10%). You trade off your ability to dodge (among other things like weapon swing speed, and spell effectiveness) for more damage mitigation.
So with all skills involved being 100 (or really just the same so all could be 50) resulting in a 50%, the two extremes would be you with a weapon skill of 100 vs their dodge skill of 1, block of 1 and parry of 1 giving you a 99% to hit, and your weapon skill at 1 vs their 100's resulting in a 99% chance to miss. Of course, increases in a skill is based on more than just what level its currently at but also at what the skills of your opponent is at too.
Then there is you and a companion attacking one enemy. The defenses would then be divided up. Each one can only work vs one opponent, therefore, your companion could have a 35% to miss (vs the npc's block and dodge) while you have a 15% to miss (vs the npc's parry).
As far as the player goes, there simply isn't enough buttons to assign to cover it all so the player could be subject to the same. Ideally the player would have control over all these things but realistically it just isn't mechanically feasible so the game is designed to do it for you based on your character's skill.
The real problem was animation. As stated, from the moment you begin to attack (or have an attack against you), the game need to calculate the path of the weapon. The game would then have to make all necessary calculations to determine the outcome (if you hit or miss), and find out how you miss if you do so. Then the computer would have to come up with the appropriate animation (the thing that Morrowind lacked that people really have a gripe over). All done before your, or the enemies, weapon takes the pecalculated path. But to be honest, if there are only z number of paths for weapons to take because there are only x number of weapons and y ways to swing them, then the game really only needs to know x and y. x being the weapon you have equipped and y being the attack (standing power, forward normal, sideways power, etc.) and the computer would have no problem determining the predicted path (z) for which the game will have an npc animation paired up with each possible z.
Of course skill would also work as it does now with the higher the skill the more damage you can do or the more armor a shield provides etc.


Skill > Chance.
