Just skimming a review of Monte Cook's Numenera, and I was struck how the Players do all the die rolling - at least in combat.

Anyone tried this in 5e?

" Thravnar ... you've got a higher initiative than the 3 Glunlings trying to bite your face off - roll your attack ... 15? That hits - their AC is 13 for future reference ... and 12 points of damage with your Enchanted Maul of Whacking? ... OK, one of the Glunlings goes down! ... now roll the other two Glunlings' attacks against you: +3 to attack and 1d8 bite damage .... ooooh ... that looks like it hurt! ..."

Yes it ends up giving the players the creature's combat stats - but I'm of the opinion/camp that an experienced fighter would have a pretty good informal "feeling" about the relative attack/defense strengths of an opponent after a round of combat, or two, anyways.

So - in-my-never-to-be-humble-opinion - it doesn't change any of the game outcomes,  gives the Players an increased sense of Agency, keeps them involved in the combat outside of their turn, and doesn't really give the players any more information ( plus I'm not sure them having information is bad anyways ), and takes a lot of workload off the DM.

An interesting variant might be to have Player A roll for the opponents attacking Player B, and vice versa.

Thoughts?

EDIT

Bouncing this idea off of my wife, who is also one of my Players, she thought it was a bit odd, since all her rolls are "about her", not about other agencies in the Universe.

So ... mathematically, you can invert this to a "defense roll"

For a PC with an AC of 14, a creature would need to roll 14,15,16,17,18,19, or 20 to hit - or 7 of 20. This means the Player-Character would need to beat a 7 on a "defense roll".

( 21 - Player AC + Creature Attack Bonus ) = Defense Roll; 21-14+0 = 7

Alternatively, 22 - Player AC + Creature Attack Bonus = Defense Roll; 22-14+0 = 8, with 8 being the Defense DC (meet or beat).

If the creature had a +3 to attack, then ( 22 - Player AC + Creature Attack Bonus ) = 22-14+3 = 11, Meaning the player needs to roll an 11 or better to defend.

This is mathematically equivalent, but switches the psychology  - the player is not making an attack roll for an opponent, they are making a defense roll for themselves.

" Thravnar ... you've got a higher initiative than the 3 Glunlings trying to bite your face off - roll your attack ... 15? That hits - their AC is 13 for future reference ... and 12 points of damage with your Enchanted Maul of Whacking? ... OK, one of the Glunlings goes down! ... now roll your defense against the two Glunlings' attacks against you at -3 with 1d8 bite damage .... ooooh ... that looks like it hurt! ..."

If the creature has advantage to attack, that means that the PC's defense roll is made with disadvantage, and vice-versa.

Thoughts?

I think you're adding maths that serve no purpose. You roll for an attack because you are making an active decision to do something. You don't roll defense against attacks because your AC takes care of it. If you treat defending as a roll you're defeating the point of having AC and eliminating dodge actions and many other defensive tactics.

I see no reason to change things. You as the DM decide what info to give to your players. From my experience it typically goes:

DM: "Dave it's your turn, what would you like to do?"

Dave: "Attack it with my great sword!"

DM: "Very well, make your attack."

Dave rolls. "With my attack bonus I got 16."

DM: "You swing your great sword and manage to hit it in the shoulder! Roll your damage."

Dave rolls. "I got 10 damage."

DM: "It was a mighty blow and the creature looks quite wounded, but it still holds up and it's now its turn! Naturally, Dave, it goes for you snarling angrily as it swipes at you with it's long black claws." DM rolls behind the screen. Checks notes on characters' ACs. "It swings wildly but manages to catch you in the side, a claw able to just get in under your armour. You suffer," DM rolls behind the screen, "14 damage. Ouch, that claw really hurt!"

I rarely come across a DM who just outright says what creature they're facing unless the group has already encountered or learned about the creature and there's no reason for a DM to just outright tell you what the creature's AC is or their health. They may describe things like "it just hits", "it missed just barely", "your arrow flew wide" and so on which can let them work it out - this is more fitting as the players must assess their effectiveness and the enemy's abilities. Telling them the AC and attack bonuses is like "here's how to defeat this" - where's the fun in that?

I see no reason to change this and your idea involves greater math and to be aware of more factors which, in my opinion, is unnecessary and detracts from the fun. It would also involve rewriting a lot of features. Seems silly to me. Combat in 5E works well. If you don't want your players to know the attack rolls the creatures are making or what their AC is simply don't tell them. It's not like your way stops them from finding out anyway through battle.

You're the DM and you can do whatever, but if you were my DM and tried this I'd leave the game.

Adds more math?

It makes a player  do one sum. Once ( 22 - your AC ) until such time as the AC changes. 

Then you roll an additional combat roll for the attacker ( or in this case, you as defender ).

I did not once say anything about telling them about the creatures name, or health, or anything else.

If you like, you don't even have to tell them the attack bonus - that just pushes subtracting the creatures' hit bonus from their roll to see if it pushes the roll below the PC's defense rating.

You are also fully free to describe the attacks and misses, as dramatically as you see fit.

As for "it spoils the fun if you tell them the AC"? I am outright robbing them of the fun of tracking every hit and miss, and trying to deduce the AC on their own. Like I've seen every gaming group - ever - do. Maybe some people derive their primary enjoyment from the game from the statistical analysis aspects, but I've never met any. I already tell my players the creature AC after their first successful hit - the character would have a rough idea of how hard the creature is to hit at this point, why would the player not?

My players already are simultaneously rolling attack and damage dice to streamline combat. Your exchange with Dave takes you 7-8 back and forth statements. This takes 2 player rolls, and detracts not one whit from the dramatic description. 

DM: Dave, your attack

Dave (making a single roll of two dice): I carry the momentum of the last attack around, using the momentum of my Greatsword, bringing it down on the adjacent creature - 16 ..

DM: Hits!

Dave: ... for 10 points of damage

DM: You catch it in the shoulder, a mighty blow, rocking it back from the force of the blow, and it looks quite wounded, It goes for you snarling angrily as it swipes at you with it's long black claws...

Dave (making a single roll of two dice): I dodge! ... 8 with a DC of 7?

DM:  You would normally be able to avoid such an attack, but the creatures fearsome strength batters down your shield, it's claws just able to just get in under your armor...

...

You could even have Dave roll all 4 dice simultaneously ( attack, damage, defend, damage ), and then just concentrate on the dramatic back-and-forth of describing the combat.

Dodge action - or Monk patient defense - adds disadvantage to the attacker roll in normal combat. In this case, it adds advantage to the defense roll.

Reaction dodges can be a follow up roll, if taken ( "re-roll your defense" ). Inspiration can be rolled and added after the initial roll as well ( "suddenly buoyed up by the Bards song you deftly dodge out of the way of the attack which you were sure was going to hit you!" ).

I don't see anything being lost here.

So:

1. Not more math, unless you count the "do 22 - X" once per armor class changes.
2. Doesn't give the players anymore information than they are already tracking on their own - or doesn't need to, if you want to do the "attack bonus" subtraction in your head as the DM.
3. If you're doing the attack bonus subtraction this only makes the player be aware of one additional number which doesn't change until and unless their AC changes;
4. Doesn't take away from dramatic description potential in combat.
5. Doesn't require reworking of dodges, or other defense mechanics; may alter when they are rolled and applied, slightly
6. Potentially gives the players a greater sense of agency, as they're no long being passively pummeled, but are actively defending.

There have been a bunch of Unearth Arcana articles back in 3rd edition about this.
It's not really a lot more math.

Basically instead of AC being 10+Armor.  The Monster has a static attack and the Player rolls 1d20+Armor, if they exceed the static attack they avoided the blow.
Players can roll to "attack" the Saves of monsters.  Lets say a Cleric uses "Turn Undead" on 6 Zombies.  Instead of the 6 Zombies trying to hit the Player's Spell Save DC with a 1d20-2, the Player attacks their static Wisdom Save of 8.
It comes out the "same", but to me I feel like the Player gains more agency.  I personally would rather roll an attack then give a monster a save.  The math is the same, but as a player I feel like I have more control when it's my dice.

Advantage and DisAdvantage all work as normal.  A Dodge gives the Player Advantage on their Defense roll, instead of the Monster Disadvantage.

If you can dig up a copy of unearthed arcana 3.5 in your local gaming store's used book's bin, there is a lot of interesting stuff and some of it translates into the current edition.

As a node, 4th tried this a lot.  A Wizard would Attack the Reflex Defense of an enemy, instead of the Enemy making a Save vs the Wizard's static attack attribute.

You do NOT need to do Subtraction!!!!  We got rid of TACO a long time ago, no one needs to make math unnecessarily hard.

Quote from FullMetalBunny >>

Basically instead of AC being 10+Armor.  The Monster has a static attack and the Player rolls 1d20+Armor, if they exceed the static attack they avoided the blow.

And - of course - there's a 5e Unearthed Arcana post for this: http://media.wizards.com/2015/downloads/dnd/UA5_VariantRules.pdf

This topic is old, but I've been doing this with my players and they love it. It keeps them more engaged in combat.

I use this for magic users as well- they roll a check adding their ST modifier and then they go up against 10+ the save on the monster side as a fixed DC

I use a table for groups from the DMs guide to tell me how many monsters make their saves on a area affect spell, and when their are too many monsters of different types (with different ST types), I just have the player roll the ST and then roll all the monsters against that number

I find it speeds up combat for me, so I can focus on describing the combat rather than math. It's fantastic.