I don't want to factor in if armor is worn or not and what kind or if even armor proficiency is a thing.  Not debating whether armor class is a good system or not - I'm writing my own system and approaching this differently.

Some of you may have experience with using shields or have studied history - that is more what I'm interested in.  Thanks.

A shield might slow you down if you're jumping around like Inigo Montoya during a fight, which would be an argument to reduce the dex bonus, but I think dex would also help you maneuver your shield effectively to an extent that would more than make up for the difficulty.

This is a pretty vague question in my eyes. There are many different design goals you might have, and the ability of the mechanics to express those design goals can depend on factors we can't know.

For me, I think the approach that's most likely to result in a good variety of build options while also keeping math within a reasonable range is to allow a player to take either a Dex bonus or a Shield bonus, but not both. Linear stacking of both is pretty likely to cause issues.

If desired, you could also handle this simply giving each shield type a property for maximum Dex allowable. This would give you the option of having a buckler benefit from Dex, but diminishing or eliminating its impact for more protective shield types.

Have you seen Advanced Fighting Fantasy 2nd ed.?

If you get hit, you roll a d6 and compare it to a table to see how many points of damage you block, depending on what kind of armour you're wearing. Dodge skill is just another kind of armour, and only works if you aren't wearing physical armour. (I don't recall offhand if you can use it with a shield but I think probably not.)

As an aside, I think I've realised one reason why I like rules-light games: it imposes a discipline against rules bloat. But that is another topic entirely.

As Matt Easton would say, depends on the Context!

In a shield wall, the benefits of a big shield aren't much affected by high DEX.

In a duel with a smaller shield or buckler, high DEX is extremely useful - the shield needs to be in the right place at the right time, just as much as your primary weapon. And a shield *is* very much a weapon; an active tool of defence and offence.

In a typical RPG skirmish, full DEX.

Hopefully this will add some context.  Designing a d20 rules light fantasy RPG, want to preserve some realism, but want system speed more.  Armor absorbs damage.  Class, Level, and Dex all factor into defense (like D&D AC).  Looking at if the benefit of a high dex allowing you to avoid harm will be somewhat lost because of carrying around a metal rimmed, wooden shield in a fight.

I want to look at the realism piece first and then try to fit that within the confines of the system.  Thanks for the input so far.

If you want to keep those kind of stacking issues simple in the game, then it is more an aspect of the underlying math of the system than anything else.  Since you are building the system, you can set the math to get what you want.  You want really simple stacking, then you need math that will accommodate it, which probably means you want to be careful on setting the lower and upper bounds of armor, shields, Dexterity, and anything else that contributes to defense (e.g. magic bonuses).  Conversely, if you want to have a wider range, then either the mechanics that handle the interaction of offense/defense has to account for that or you need more involved stacking rules.

Also consider what you are abstracting.  If the role of defense of the shield in the game model is a mixture of movement, passive blocking, and various offensive threats all rolled into one number, then you can treat small shields and large shields as pretty much the same thing--perhaps with some edge case footnotes for bucklers and hoplite style shields at the extremes, especially if the edge cases are such that they won't be selected often.  The increased maneuverability of the smaller shields compensates for their lesser coverage.   On the other hand, if you make those various elements less abstract, then there is a notable difference in what parts of the model the shields will contribute to, and bucklers and hoplite shields are almost as different in the model as daggers and polearms. 

So I guess max simulation would be:

1. full DEX for small & medium shields.
2. Either half DEX for large shields, or full DEX+the small shield bonus if better than half DEX + the largeshield bonus.
3. no DEX for Pavise/Tower shields (ie just use whichever bonus is better).

Large shields & especially Pavises should have a really good bonus vs missiles though.

If I were looking to limit the characters' maximum dex bonus for the sake of realism, I would use encumbrance in general, and not shields specifically.

Is you dex better when holding a big sack of gold than it is holding a shield? If anything, it seems to me that the opposite would be true, since shields are literally designed to be wielded in combat, and they even strap onto your arm.

As a former dark age reenactor I can confirm that an agile guy with no armour and a shield is a pain to fight, he's either not there or has his shield in the way.

There's a reason that shields were common until armour got good enough to make them superfluous.

A shield can take a lot of forms.  A pavise is one of the largest versions and was usually staked to the ground.  If you dodge away from it using your superior dex, you're not going to take advantage of it. 

Dexterity/Agility/Evasiveness generally allow you to move out of the way of an attack.  Small things are dodgier.  Shields are big things, and therefore they make you a bigger target.  If hitting the shield is the goal, you're easier to hit because you're holding a shield.  Even if you dodge your body out of the way, the big shield is hard to ALSO move out of the way. 

But the nice thing is that shields were designed to be hit.  If you can safely move yourself entirely out of the way with a quick back-step and you and the shield are completely missed, great.  But most of the time, you're moving your vulnerable bits out of the way and putting the shield IN THE WAY so it gets hit, but your vulnerable bits don't. 

Ultimately, I think that a shield, being big and heavy, tends to limit your ability to dodge out of the way - but not to the point of completely negating it. 

Quote from: deadDMwalking on August 20, 2021, 02:15:54 PM
Ultimately, I think that a shield, being big and heavy, tends to limit your ability to dodge out of the way

Not much. And more importantly, it blocks line of sight, which can make the skilled wielder much harder to hit - but can also hinder the unskilled wielder's attempt to parry.

Quote from: S'mon on August 20, 2021, 04:13:25 PM

Quote from: deadDMwalking on August 20, 2021, 02:15:54 PM
Ultimately, I think that a shield, being big and heavy, tends to limit your ability to dodge out of the way

Not much. And more importantly, it blocks line of sight, which can make the skilled wielder much harder to hit - but can also hinder the unskilled wielder's attempt to parry.

  I do wonder if we had a 20 year veteran of the legions from Rome around, I wonder what sorts of things he could share?  I remember reading an account of a soldier who had his arm hacked off fighting pirates during a ship to ship fight.  The story was that he then went on to kill or knock overboard a dozen men with his shield.  The Scutum was designed to be used as a weapon as much as defense, and even a good deal of sculpture and art show the soldiers bashing opponents in the face before stabbing them in the gut. 

Shields are amazing weapons. 

But that's not really the point.  A shield is interposed between you and the enemy, becoming the target instead of you.  In a lot of historical fighting, you stood next to someone else, your line pushed shields against someone else's line, and you hacked at whatever you could.  But that's not what we're usually modeling in D&D. 

Facing rules are a pain.  Someone with a shield is almost certainly harder to hit than someone that doesn't have a shield.  But someone wearing heavy armor and a shield isn't going to be weaving and dodging between opponents in the same way that a wuxia film shows. 

  Heavy armor is amazing protection from harm.

  But that's not really the point.  The point is would the shield ALONE affect dexterity.  I think it would get a full bonus from dexterity.  A coordinated person with great reflexes is not going to be slowed down in a meaningful way related to combat at all.

   Regarding historical fighting, that is NOT how a lot of shield users fought.  The Celts for instance did not fight in strict formations. Gauls did not fight in strict formations Neither did the German barbarians. Nor did the Homeric heros of greece. Many historical shield users did not fight that way.  MOST of them fought exactly as modeled in D&D, alot of this was cultural in high value of individual valor and lack of central command and effective command methods on an active battlefield; we know this because most of them LOST to the guys who did fight in tight formations (Classic greeks and the Romans). Most also did not have heavy armor, and many like the celts and gauls fought naked. But they all used shields, and primarily for missile defense, because you are not cutting or stabbing anything if sling stones or arrows took you out as the enemy closed.  Our perception is that most fought this way because the images we see most are Hoplites and the Legions, and that is because the winners write history.