A lot of people have helped me with their input here.  Thanks!
I'm trying to pen a fairly fast d20 fantasy system - not crunchy.  I like moderately gritty & dark.

Combat: Roll to hit, roll for damage, subtract armor's damage absorption (static #).

I'm scrapping AC in favor of ES (Evasion Score - until I come up with a better name) to help determine target number to hit opponent. 

Armor will not contribute to ES, rather it will absorb damage (DA = Damage Absorption - until I get a better name).  I've run what I think is a lot of math on this and like how it works within the parameters of the rest of the system.

My current stumbling block are shields.  I don't want shields to add to ES.  Likewise, I don't want it to add to DA.  Do you have another idea that does not involve creating another die roll?  Thanks.

What are you trying to simulate or model with shields that doesn't involve either avoiding getting hit or reducing damage? Other than things like a shield bash or maybe setting up a block/counter strike, that's pretty much it, and those are secondary to the protection aspects.

Quote from: Vic99 on August 10, 2021, 02:52:55 PM
A lot of people have helped me with their input here.  Thanks!
I'm trying to pen a fairly fast d20 fantasy system - not crunchy.  I like moderately gritty & dark.

Combat: Roll to hit, roll for damage, subtract armor's damage absorption (static #).

I'm scrapping AC in favor of ES (Evasion Score - until I come up with a better name) to help determine target number to hit opponent. 

Armor will not contribute to ES, rather it will absorb damage (DA = Damage Absorption - until I get a better name).  I've run what I think is a lot of math on this and like how it works within the parameters of the rest of the system.

My current stumbling block are shields.  I don't want shields to add to ES.  Likewise, I don't want it to add to DA.  Do you have another idea that does not involve creating another die roll?  Thanks.

   By chance have you looked at something like Conan D20 for ideas around this?   In that game armor blocked damage, and how hard you were to hit was based on your choice of using a parry or dodge stat for your class (warriors for example had high parry and lower dodge, and thieves had lower parry and higher dodges).  Parry was modified by your strength bonus, and could not be used for missile weapons coming at you.  Dodge was modified by your dexterity and could be used against missile attacks.  Shields added a bonus based on type of shield as to what defense you were using. 

   I think Monte cook had a game similar to this (Iron heroes?) where in addition to a "to hit" bonus classes got a Parry and Dodge bonus that grew with their levels as well.   Since you are abstracting defense already, I think the smoothest thing to do is to simply add the shield bonus to the preferred defense the player is using.

Steven Mitchell said, " What are you trying to simulate or model with shields that doesn't involve either avoiding getting hit or reducing damage?"
  I see armor as a layer of protection that is either penetrated or not.  I know an attacker could bypass it - scoring a hit in an unarmored area - but I'm not going to get into hit locations.  It just doesn't feel right to have a system that says: Armor X absorbs/prevents the first 3 points of damage, but Armor X + Shield prevents the first 4 or 5 points instead.

Oggsmash, saw a Seth Skorkowsky review of Conan, but haven't read it or played.  I probably won't do parry or dodge., it will add another step.  Plus ES will cover that.

You don't want shields to add to defence. Not even an alternate defence like Parry vs Dodge.
You don't want shields to reduce damage.
You don't want an extra die roll shield 'save' (as in Dragon Warriors & Warhammer).

Err... 

I think you may be out of luck.

S'mon, I'm trying to see if I'm missing something.  Perhaps not.

With a bit of googling, Warhammer rpg seems to let a player use a shield to cancel out a critical hit.  That might be something I can work with.  Or maybe I have to treat it as partial cover.

Quote from: Vic99 on August 10, 2021, 02:52:55 PM
My current stumbling block are shields.  I don't want shields to add to ES.  Likewise, I don't want it to add to DA.  Do you have another idea that does not involve creating another die roll?  Thanks.

My favorite hack is to give shields a block ability, usually to cause an attacker to re-roll a sucessful hit. But you said you didn't want another dice roll, so not sure if that counts or not.

Quote from: Vic99 on August 10, 2021, 05:13:46 PM

Steven Mitchell said, " What are you trying to simulate or model with shields that doesn't involve either avoiding getting hit or reducing damage?"
  I see armor as a layer of protection that is either penetrated or not.  I know an attacker could bypass it - scoring a hit in an unarmored area - but I'm not going to get into hit locations.  It just doesn't feel right to have a system that says: Armor X absorbs/prevents the first 3 points of damage, but Armor X + Shield prevents the first 4 or 5 points instead.

Oggsmash, saw a Seth Skorkowsky review of Conan, but haven't read it or played.  I probably won't do parry or dodge., it will add another step.  Plus ES will cover that.

  It is not another step, but I think if you were to take a look at it, you can decide how to amalgamate parry and dodge for each class into just one number.  But it does not add a step as is.  Not sure what you mean by adding a step.  It does give the player an option to use their dodge or their parry, if that is what you mean by step.

One thing to bear in mind is that there is NOT actually a significant increase in complexity by having two or more defense categories to check against vs. just one.

If an attack is "roll a d20 and add your attack bonus then compare to a defense target number" then the only increase in resolution time for multiple defenses (ex. having a "Parry" and a "Dodge" vs. just "Defense") is the slight time it takes to locate the Parry number or Dodge number on the sheet vs. just locating the Defense number. Once you've located the number its still just "is the attack number greater than or equal to the target number?"

Ergo, having a Shield Defense (for attacks a shield would be useful in deflecting) and an Evasion Defense (for attacks a shield wouldn't help with) isn't going to increase resolution time by any significant amount.

Generally speaking, making yourself harder to hit is usually worth more than Damage Absorption, unless the DA can negate a hit... 

For example, take two characters; A is hit with a 16+ and has 0 DA; B can be hit with a 11+ and has 5 DA.  Assume the average damage is 15. 
In that case, the total damage over 20 attacks against A is 75 (5 hits).  The total damage over 20 attacks against B is 100 (10 hits for 150 damage, minus 50 damage).     

If damage is lower (say 5), character A takes 25 damage (5 hits) and B takes 0 damage (10 hits for 50 damage, minus 50 damage). 

If you know how damage scaling works, you can determine what is optimal in your system.  If there are rider effects beyond damage (like stunning), not getting hit is even more valuable than absorbing the damage. 

I'd recommend doing the math to make sure that it works the way you want. 

Generally, it'll be EASIEST if shields impact one or the other.  If you initiate an alternate rule like 'someone with a shield can force a re-roll for a successful hit', that really just becomes another way of applying a bonus or penalty.  If you went with that, Person A is only hit 6 1/4% of the time (instead of 25%) because each time a hit is scored they have to roll a hit AGAIN and Person B is only hit 25% of the time (rolling an 11+ twice in a row).  But there's not much difference between just calling it a +4 EV bonus.  For person A, if their opponent needs a 20 to hit (instead of a 16), they're going from a 25% of taking a hit to 5%.  For person B, if their opponent needs a 16 to hit (instead of 11), they're going from being hit 50% of the time to being hit 25% of the time. 

Creating a rule that emulates a specific bonus might be more flavorful, but in terms of the impact to expected results it might very well be covered entirely by bonuses/penalties to your existing resolution system. 

Good suggestions.

Ratman: "My favorite hack is to give shields a block ability, usually to cause an attacker to re-roll a sucessful hit."
Going with a reroll is out, but I appreciate the idea.  Sometimes ideas that I don't like lead to one that is useable and I never would have thought of it in the first place.

Oggsmash: " . . . you can decide how to amalgamate parry and dodge for each class into just one number."  and
Chris "If an attack is "roll a d20 and add your attack bonus then compare to a defense target number"

This is essentially how Evasion will work.  It is a function of class and level.  Different progression for different classes.  Increases with level.  A guy's evasion is the target number to hit him.

Deaddmwalking: "If you know how damage scaling works, you can determine what is optimal in your system.  If there are rider effects beyond damage (like stunning), not getting hit is even more valuable than absorbing the damage.
I'd recommend doing the math to make sure that it works the way you want. "

In order to work out both Evasion and DA, I ran through the math for different die types and combos (like 2d6) - averages, min, max, as well as how that changes with common DAs.  I feel pretty good about it, but expect that play testing will show if I nailed it or it needs to be tweaked or scrapped.

These are all great points and pieces of info to consider.

Deaddm:"Creating a rule that emulates a specific bonus might be more flavorful, but in terms of the impact to expected results it might very well be covered entirely by bonuses/penalties to your existing resolution system."

I'm coming to the conclusion that this may be part of it.  I wanted to someone could point out a mechanic that I'm missing.

I leaning toward going with shields giving +1 to Evasion, but the player has the option to make the shield negate one hit and have the shield be destroyed.  Perhaps shield attacks will be developed too, but not worried about that.

Sometimes taking the long way home makes you realize that the imperfect shortcut is still really good.

Something else to keep in mind about shields and armor is that both were often designed in such a way as to cause blows to glance off them... that would basically fall into the "not hit at all" part of your rules since minimal kinetic energy is imparted do the the weapon glancing off the slope of the pauldrons, etc.

One thing worth mentioning since I recently started playing in a Spycraft campaign is how their armor works since its actually similar to the above; Armor typically provided a mix of both a very low bonus to Defense (typically only +0 to +1 on the armor itself +1-2 if wearing a helmet) indicating the armor's ability to cause various attacks to glance off without penetrating AND a Damage Reduction score indicating how much of what didn't glance off would be stopped.

Ex. Kevlar BDU's + Ballistic Helmet were good for a total of +3 to Defense (+1 from the BDUs, +2 from the helmet) and DR 5 (or 7 with inserts).

This mix and match would give you another axis on which to model armor... something like chain doesn't have ANY defense to speak of because its not built using rigid materials to deflect blows... it would be +0 defense, 3-4 DR. Adding a conical helm though might add +1-2 to defense since many blows to the head will be deflected because that's the entire point of the conical shape.

Something like a full plate harness though with its many curved and angled plates designed to cause weapons to glance off might offer +3-4 defense vs. weapons in addition to any DR.

Shields in this system were almost entirely of the "improved defense" variety as the primary means of using them was not to take the blows full on, but to get the weapon to glance off the shield just as it would off the many curves of a full plate harness.

In the system we use, armor provides both a bonus to defense and damage reduction.  We differentiate between attacks that you're aware of (normal defense), unaware of (flat-footed defense) and those that just need to connect (touch).  Shields provide a bonus to normal defense and touch, but not flat-footed.  Armor provides a bonus to normal and flat-footed defense, but not touch. 

If your system doesn't distinguish between types of attacks in that manner, you couldn't use that, but if you have categories of attacks, choosing some that shields apply to instead of armor may be helpful. 

Quote from: Vic99 on August 10, 2021, 02:52:55 PM
My current stumbling block are shields.  I don't want shields to add to ES. 

Why? That what shields and for weapon parrying do at the end of the day. They reduce the odds that the opponent will not hit their target.

For example GURPS which has an explicit defense roll.

Able has a Broadsword skill of 15
Baker has a Shield Defense of 11.

The odds of Able landing a blow is 95.37% (broadsword odd) times 50% (shield defense odds)  is 47.68%

Now you are not using a bell curve so it easy to eliminate the defense roll. Just divide the impact that shield would have as a defense roll and add that number to your Evasion Score. The odds of landing a blow with a single attack roll will be exactly the same as as the attack roll and defense roll.

As S'mon said your options are limited given your combat resolution system.

Now as mention else in this thread you could give shield a limited number of automatic defense. But that doesn't reflect how it would look if you were there witnessing the action.

There is no cap beyond fatigue to the number of times you can trying to interpose a shield between you and an opponent. Or using the same shield against multiple opponent.

Sure you can try to to say using a shield for defense is that tiring. But then why are not weapons that tiring as well. So the result feels like a boardgame construct divorce from the setting. Even if something fictional I can't think of any depicting of combat with shield where the wielder is limited in the number of time they can use the shield.

You could try to say that the shield can only be used X time to negate a hit before being splintered. That is a little better but you will have to fiddle with the numbers to get the right feel. Even then I suspect it will have to be high.

And you will quickly run into smart players that will game the mechanic to make sure they have a fresh shield on hand at all times. Because negating a blow is a really good option to have. But this behavior does not reflect how shields were used in life or in most fiction.

GURPS got rid of passive defense for armor which added to the character's defense roll. Instead they made skill more important for defense rolls, but they still kept a defense bonus for shields because that worked best for how shield actually worked.

Also note that in the variant rule for D&D 3.5e. Armor as Reduction shield still gave their full bonus.

https://www.d20srd.org/srd/variant/adventuring/armorAsDamageReduction.htm#shields