Talysman has been discussing house rules for dodging. This was one of his proposals:
A character can try to dodge an attack from a single opponent per round if the character’s Move rating is higher than the opponent’s Move rating. The character takes damage only if the damage is greater than a 1d6 roll.
The essence of this rule is a form of variable damage reduction. Assuming d6 damage, since this is OD&D, this means that characters with higher movement scores (compared to an attacker) will dodge 21 out of every 36 attacks (this is based on enumerating all 36 possibilities), and damage taken has an expected value of approximately 1.94 (compared to the expected value of 3.5 damage in the case with no dodging).
I don’t love the necessity of another die roll for the dodge, but I am intrigued by the idea of basing some form of damage avoidance or dodging on comparative movement scores, as that fits thematically and potentially makes encumbrance that much more important. Yes, mathematically it is always possible to model any kind of defense as a bonus to AC, but that also feels somehow unsatisfactory in this domain (and tends toward systems with constructs like “flat-footed” to account for those cases where agility would not come into play).
Rather than rolling a die for the dodge, why not give an explicit damage reduction based on the difference between the two movement scores? That is, a character with move 12 would have a DR of 3 when attacked by an enemy with move 9. No extra dice rolls required, and the expected end result is somewhat similar. Any damage result less than this threshold would indicate a successful dodge. This DR would only apply to melee combat (though I could see a class special ability extending it to missile attacks as well, perhaps for a martial arts class like the monk). This also has the added benefit of distinguishing between an attacker with move 9 and move 6 (which would be handled identically in Talysman’s system, assuming the defender had a movement higher than 9). This also means that characters with very high movement rates would be virtually immune to the attacks from slow creatures. This is not necessarily a problem, though it would be reasonable to cap the dodge-based DR (perhaps at 4 or 5) to maintain a higher level of risk.
I’m not sure I would actually use a rule like this in play, as I’ve found such added defense rules to be particularly easy to overlook in the heat of combat, but that said this form of comparative damage reduction seems rather attractive.