This is an optional rule for increasing the usefulness of shields in d20.
When using a shield against an opponent who does not have a shield (bucklers do not count for this), add the shield AC modifier to your attack rolls against that opponent.
Modeling the versatility of the shield in this case it is about stressing its usefulness when one is fighting another who has no shield. The shield can take & deflect blows, and because of this allow effective counter-striking; since one has much better protection against sneaky things like sliding over the ricasso.
Try it out in your next d20 game and tell me what you think. Suddenly that 2 or 3 points of shield AC becomes very useful against all those beasts with stupidly high “Natural AC” bonuses.
Shields are great – particularly when your opponent doesn’t have one. There’s a few ways to better model this in d20-based systems (like DnD, OGL, SRD, etc).
1. Instead of the shield’s AC bonus you can use the shield to “soak” damage. Convert the shield’s AC bonus to Damage Reduction. You become easier to hit but harder to damage. This is the willingness to take a hit on the shield.
2. Forfeit the AC bonus of the shield. Instead make a roll to “soak” the damage with the shield if you are struck. In v3.x roll vs. a DC of 10 + Opponent’s BAB + weapon specialization (and the like). The shield-wielder adds their BAB + shield specializations (and the like). Each point of success reduces the damage by an extra point.
Eg. DC is 19. Roll a total of 21. Reduce damage by 3 (19, 20, 21).
2a. Shields can be given a maximum damage they soak before they “splinter”.
Eg. a buckler might be able to soak 15 damage before it splinters (is made useless).
3. When one has a shield and the opponent does not double the AC mod.
The point here is that with a little bit of thought shield function can be better reflected in any system.
(Image from: http://etc.usf.edu/clipart/58600/58671/58671_kite_shield.htm )
The shield; oft whined about, oft under-rated, and mostly ignored as something that is uncool. In DnD/d20 the shield can reduce your chance of being struck by 5% for a buckler to 20% for what that game dubs a tower shield. Unfortunately that’s not a the only thing a shield does. It might just be the most obvious one to an external observer.
Those of us who took our asses to the real side of life and found out what the weapons were, read history, and checked our facts in martial sciences realised a shield is a weapon. It’s not a lethal weapon, per se, but it is a damned fine complimentary weapon. In short the shield aids a character’s ability to melee.
Many systems separate the skill of attacking from the ability to defend; or even make defense something that is based on pure natural ability and hardware with nothing to do with skill at all. This is not the way it works. The two, attack and defense, are inextricably tied together.
Modelling this in an easy way was elegantly done in Simple 2d6. The skill for Melee covers attack and defense simultaneously (see this post). From there it was very easy to model shields as aiding the fighter’s combat ability with a bonus to Melee. With larger more robust shields the wielder also gets a bonus to their armour value. So simple it’s beautiful.