Kainenchen and I have been talking about the economy of actions in D&D Next lately, particularly in light of the fact that most characters have no way to spend their reaction in a round unless someone provokes an opportunity attack. Further, D&D Next needs more movement in combat (since we play with TacTiles and minis anyway). While LARP combat is definitely not true simulation, it has repeatedly shown me that a fighter or shield-wall with room to fall back can avoid a lot of hits. With these and other examples in mind (such as the constant movement of swashbuckling duels in film), I propose the following:
As a reaction, whenever you take damage from a melee weapon attack or a weapon-like spell (such as flame blade), you may move five feet away from that attacker in order to reduce the damage of the attack by 1d6 hit points.
The attacker has the immediate option to move five feet to follow, though if the attacker has caused more than one opponent to Give Ground in the same round of actions, she may follow only once.
If none of the three squares behind the defender that increase his distance from the attacker are legal destinations, he may not Give Ground (even if he could otherwise pass through the square, such as when occupied by an ally).
The defender also may not Give Ground to move into difficult terrain. Situationally, the DM may find it appropriate to allow a character to Give Ground with a move onto difficult terrain with a successful skill check (such as using Acrobatics to leap backward onto a table.)
If for any reason the move backward fails, the defender does not reduce the incoming damage.
A character may Give Ground in addition to being pushed, but not when knocked down, pulled, or teleported. The character must be able to move, and (obviously) must also be able to take reactions.
I think this rule may have an interesting effect on gameplay, particularly low-level gameplay. I might find it necessary to increase the Give Ground value at later levels, but I do expect higher-level characters to be more willing to stand their ground. Importantly, the Hold the Line feat interacts cleanly and correctly with this rule - a character with that feat can either check the withdrawal of the defender or the advance of the attacker, whichever is his enemy. I am also pleased that the barbarian's rage ability (currently) prevents him from using this ability.
Obviously I'm feeling very satisfied with myself, so please, let me know what I've overlooked. I do envision this action stacking with the Parry ability, the Protect maneuver, and other forms of damage mitigation. The addition of such an action will extend combat somewhat. My hope is that the payoff in voluntary movement and use of reactions to make (relatively simple) decisions on the opponent's turn will make up for this. There might be room for additional class abilities, maneuvers, and feats that plug into Give Ground's effect.
This ability would be easy to adapt into 4e, though it may be (in a more powerful version) already a Utility power for some class or other. Were I to adapt it into 4e, I would be inclined to have the d6 scale upward at some rate.
The fact that this cannot apply (as I have envisioned it) to ranged weapon combat or ranged spell combat does provide a significant advantage to those styles, and I might consider the possibility of edging up melee effectiveness slightly or removing the restriction against Giving Ground to spells and ranged weapons, depending on how it worked out in actual play. The most simulationist answer, I think, would be to apply an inherent accuracy bonus to melee attacks and melee-weapon-like spells.