When exactly does combat start and surprise take effect?

Question

Say I'm going to ambush an orc. I successfully sneak up on him and I attack. The DM determines that the orc is surprised. The orc happens to get an initiative roll of 19, while I get a 10. How would this work? I can only think of two reasonable resolutions to this.

1. The orc, having a higher initiative, goes first. Since he's surprised, he does nothing. Then it's my turn. If the orc survives my attack, it is now his turn, and being that the orc has already gone through his round of surprise, he can now attack me or whatever, and combat proceeds as normal.
2. I, having started the combat, go first. If the orc survives my attack, but he is surprised, so he does nothing. It is now my turn again, I attack again. If the orc survives my second attack, it is now his turn, and being that the orc has already gone through his round of surprise, he can now attack me or whatever, and combat proceeds as normal.

Which one of these is correct? neither? Does starting combat secure me a turn/action at the start of initiative order like in option 2? If option 1 is correct, could I ready an action to shoot the orc, effectively granting me a similar first attack as in option 2?

Sorry if this makes no sense.

Answer 1

Interpretation 1 is correct.

The rules for surprise state:

The DM determines who might be surprised. If neither side tries to be stealthy, they automatically notice each other. Otherwise, the DM compares the Dexterity (Stealth) checks of anyone hiding with the passive Wisdom (Perception) score of each creature on the opposing side. Any character or monster that doesn't notice a threat is surprised at the start of the encounter.

If you're surprised, you can't move or take an action on your first turn of the combat, and you can't take a reaction until that turn ends. A member of a group can be surprised even if the other members aren't.

Surprise occurs within initiative, as noted in the "Combat Step-by-Step" sidebar in the "The Order of Combat" section:

1. Determine surprise. The DM determines whether anyone involved in the combat encounter is surprised.
2. [...]
3. Roll initiative. Everyone involved in the combat encounter rolls initiative, determining the order of combatants' turns.
4. [...]

If you declare a combat action (e.g. an attack), you roll initiative before the combat action is resolved. If a creature is surprised, that simply means it can't take actions (or bonus actions, since "anything that deprives you of your ability to take actions also prevents you from taking a bonus action") on its first turn of combat, and it can't take reactions (such as opportunity attacks) until its first turn is over.

Any combat action would occur within initiative. You can't ready an attack outside of combat; otherwise, literally every character would have an attack readied as they wander around a dungeon. The point of initiative is to resolve the order in which creatures that are prepared for combat (i.e. not surprised) act.

Answer 2

Your first interpretation is correct.

Initiative is rolled as always. If the orc rolls higher than you he is still surprised and does nothing. If the orc rolls lower than you and you stab him he is still surprised and gets to act and move only in the next round.

Look at the following line from the rules on surprise:

[...]

If you’re surprised, you can’t move or take an action on your first turn of the combat, and you can’t take a reaction until that turn ends. [...]

The only difference the initiative of the orc makes would be in relation to opportunity attacks. If the orc is surprised and goes after you, you can run in, stab him and then swiftly move out of his reach (if you have enough movement left) without him able to retaliate; if, however, he did have his first turn (during which surprise wears off) before you move, you'd get counter-stabbed if you moved out of his reach after attacking.

Answer 3

RAW, Situation 1 is Correct

The rules on surprise on page 189 of the PHB (Chapter 9: Combat) state, in part:

The DM determines who might be surprised. If neither side tries to be stealthy, they automatically notice each other. Otherwise, the DM compares the Dexterity (Stealth) checks of anyone hiding with the passive Wisdom (Perception) score of each creature on the opposing side. Any character or monster that doesn’t notice a threat is surprised at the start of the encounter.

If you’re surprised, you can’t move or take an action on your first turn of the combat, and you can’t take a reaction until that turn ends. A member of a group can be surprised even if the other members aren’t.

So, whomever rolls the higher initiative still goes first. If it's the surprised creature, however, they cannot effectively take a turn.

However, the GM has the ability to change the rules in any way they see fit, and one example that I've seen some GMs do is ruling that Surprised creatures get a penalty to Initiative rolls (because they can't react as fast.)

The GM can also apply situational/circumstantial bonuses depending on the situation. For example, a Rogue attacking from Stealth with a crossbow might get an additional +2 on their initiative role, but a combatant affected by the Slow spell (such as from an Artifact) may roll with a -3 penalty.

Answer 4

By strict RAW of your question, situation 1 is correct. You have already rolled initiative, so you have to act in turn order. However, that isn't the only way your DM could have played this scenario.

Combat begins when the DM says so

There isn't any explicit guidance as to when combat encounters technically begin. We know what a combat encounter is, an encounter where we are playing in turns, fighting monsters. But the Basic Rules, the PHB, and the DMG, do not actually explain when the encounter begins. In your example, the DM has ruled that the combat encounter begins as soon as you want to attack, but that isn't the only way.

The rules actually have two example situations for initiating surprise combat:

A band of adventurers sneaks up on a bandit camp, springing from the trees to attack them. A gelatinous cube glides down a dungeon passage, unnoticed by the adventurers until the cube engulfs one of them. In these situations, one side of the battle gains surprise over the other.

The second example of the gelatinous cube is extremely relevant. The example has the cube attack before combat begins, after which the party is surprised. Your DM did the opposite, combat started before you could make the attack. They could have done this instead.

Have combat begin after the action that initiates it

Your DM could allow you to make the attack, then roll initiative after that:

• You: "I stab the orc in the back!"
• DM: "Roll the attack"
• You: rolls, hits the orc, deals some damage
• DM: "The orc grunts in surprise and pain! Roll initiative" rolls 19 for the orc
• You: rolls 10
• DM: "The orc is initially surprised, but recovers quickly, whirling around to glare at you! Your turn"
• combat continues