Defence = current movement rate in inches.
Dexterity modifies Defence.
Encumbrance reduces movement rate, which in turn reduces defence.
To hit an opponent, roll above their defence on a d20.
Armor reduces the amount of damage inflicted per damage die rolled. All successful hits deliver a minimum of 1 damage per damage die.
Leather amor -1
Shield = +1 defence, -1 damage.
Two weapon fighting = +1 defence, +1 attack per round (i.e. roll 2 d20 attacks)
eg Bob the Fighter, dexterity 13 (+1) wearing plate mail and shield has a movement rate of 6". He is attacked by a bite that may inflict 3d6 damage.
Defence = 6+1+1 = 8.
Monster rolls 9, a hit.
Damage roll for 3d6 = 5,2,6.
Armor reduces damage by -3 plate, -1 shield for each damage die (i.e. total of 4) = 1,1,2 = 4 damage.
So people who wear armor are easier to hit, but harder to damage.
Simple, I like it.
I just need to play test, next opportunity. Might even add into my Kids D&D.
Now, any idea how to make a horse, movement 24", able to be hit on a d20?
The law of unintended consequences - back to the drawing board.