How can we model "acting first" in a hostile parley?

Question

Two parties are arguing with each other, but combat has not started. Perhaps leaders on each side are trying to avoid combat, but having trouble controlling their troops. Perhaps they were interacting in a friendly manner, but someone insults someone else and an argument erupts that could lead to violence. Perhaps two sides are competing toward completing the same goal (so they are hostile) but don't want to spend resources in combat with each other. Or perhaps there's just a loose cannon on one or both sides.

Both sides are aware of the other, and both sides are aware that violence could erupt at any time. The first three steps in The Order of Combat are:

Determine surprise. The GM determines whether anyone involved in the combat encounter is surprised.

Establish positions. The GM decides where all the characters and monsters are located. Given the adventurers' marching order or their stated positions in the room or other location, the GM figures out where the adversaries are—how far away and in what direction.

Roll initiative. Everyone involved in the combat encounter rolls initiative, determining the order of combatants' turns.

As I understand the surprise rules (and please correct me if I am wrong), the combat would not begin with anyone surprised. IRL of course, the person who swings first has a slight edge, though they can be preempted by a particularly fast opponent. But my understanding of RAW is that whoever initiates combat, the initiative roll completely determines the order. Acting first in this context becomes little more than a twitch that confers no advantage.

Are there any existing rules (SRD/core, expansions, Unearthed Arcana) which can model getting the jump on a suspicious or hostile creature who is looking right at you?

As a follow-on, I would take suggestions for how to model this in a simple way that doesn't do great violence to the existing rules.

Answer 1

The DM determines whether anyone involved in the combat encounter is surprised.

Why does that mean that no-one can be surprised? It means you decide if they are. While you cannot be surprised if you aware of a threat that has to mean the threat of violence - being involved in an argument, even a heated argument, does not mean there is a threat of violence.

While normally you look at opposed Dexterity (Stealth) & Wisdom (Perception) there's nothing wrong with comparing Charisma (Deception) ("I'm not going to hit you") & Wisdom (Insight).

Answer 2

Initiative is just a DEX Check

D&D 5e has no rules for acting first beyond initiative and surprise. As you point out, if you attack someone IRL, they could potentially be faster than you and pre-empt your attack. Framing this in the context of initiative, going before your attacker just means that you won an opposed dexterity check and are thus faster.

A more concrete example:

Scenario 1: "The goblin, angered, stabs at you with a sword. Roll a dex save to get out of the way."

Scenario 2: "The goblin attacks. Roll initiative."

I'd argue that the two scenarios are identical, mechanically speaking. Just because you decide to act before your opponent acts doesn't mean that you will actually get to act first.

Alternatives include surprise and advantage/disadvantage

If you really want to give an attacker the advantage, I think the best way to accomplish this is to use surprise or the advantage/disadvantage system. As Dale M mentioned, you could replace the stealth and perception rolls in determining surprise with deception and insight, or some other set of appropriate skills. Alternatively, you could give the attacker advantage on their initiative roll (in a case where the attacker has some advantage but not total stealth) or the defender disadvantage (where they're caught off guard, for example).

The combat rules aren't just for fighting

Just because you've rolled initiative doesn't mean that a fight has begun. You can use the initiative rules to systematically adjudicate all sorts of scenarios, such as the competition you mentioned before. If you've got two teams racing toward an objective, initiative is great for determining the results of the race, where creatures can choose to dash, or cast a spell to inhibit their enemies, or whatever.

You can even roll initiative when one party member wants to fight and another one wants to stop him, for example:

PC 1: I want to punch the bartender.

PC 2: I want to stop PC 1.

DM: Roll initiative!

(Scenario 1: PC1 wins initiative)

PC 1: I punch the bartender.

DM: PC2 reaches to restrain PC1, but isn't fast enough to stop PC1 from punching the bartender.

(Scenario 2: PC2 wins initiative)

PC 2: I attempt to grapple PC1.

DM: PC2 grabs PC1's arm, trying to hold him back.

Answer 3

Advantage and non-stealth Surprise

Initiative is a DEX check, and the DM can award advantage or disadvantage whenever he pleases. The best way to model might be giving the starting party advantage, and the other party disadvantage, depending on circumstances.

An alternative is for non-stealth surprise to occur, using deception and insight checks, or even passive insight and passive deception.

The final thing that comes to mind is to give everyone advantage on their first attacks, to model the confusion of the engagement and hostility of the factions. In a sudden scenario like that with intermingled combatants, defending yourself is more difficult than attacking someone, so in the short term it's a blood bath. This also allows Rogues to sneak attack.

Having virtually every attack hit also imparts a thematic sense of wanton slaughter and brutal violence, aided by your descriptions of what the attacks are, which can be strongly evocative.

(You can experiment with more extreme versions of the above, like having certain non-insightful characters be "stunned" for the first round of combat, or simply letting every attack hit outright).