[RPG] How are Attacks of Opportunity and Reactions explained in Narrative Time


I'm not sure if the title is clear. I'll try my best to explain this problem.

In Pathfinder, when an enemy moves out of a square within your melee reach, you can perform an Attack of Opportunity (AoO).

Similarly, in Rogue Trader, you get a free attack (essentially an AoO) if the enemy you're engaged in melee with moves without making a Disengage action.

However, how would this happen if we could see the whole combat like a movie? According you RT's rules, every round lasts around 5 seconds (6 in PF I think) and everything happens more or less at the same time (not sure if that's also true in PF, but I think it is).
How can you attack in one round but at the same time perform another attack? Is that like a reflex? I know not every action happens exactly at the same time, maybe one attack follows the other by a fraction of a second, but then if you have the ability to attack twice in a round, why don't you always do that?

Another problem i have related to AoO, is when you play a game that actually lacks AoO, like Rogue Trader:

In a fight, there was an NPC who moved very fast, ran a number of squares, passing next to a PC. My players argued that since the NPC moved into melee range, his character should be able to at least react to that and be able to do some sort of melee attack, however, the rules say nothing of AoO save from those who are engaged in melee. How do you explain that someone can't do anything about an enemy who runs right next to them? You could argue that it moved too fast for him to react, but at the same time, how can a PC try to dodge a bullet, or even have an AoO with the same NPC moving at the same speed, only because they were engaged in melee?

I know there's no perfect system and no system is ever 100% true to reality, but I'm just having a hard time imagining combat as a flowing narration. Bear in mind my knowledge of PF is very basic, I'm only good at RT.

Best Answer

This is a difficulty that comes up in a lot of RPGs actually, including way back in the early editions of D&D (from which Rogue Trader gets its Disengage-to-avoid-bonus-attack rule).

Think of the round as being full of position and weapon maneuvers and potential attacks, but the roll is only made for the pivotal attack opportunity for which all the the feints and parries and ducks and weaves were softening up the enemy. In this way, the roll is an abstraction of all your careful efforts during the round. See the "Combat Abstractions" sidebar on page 234, where the rules instruct the reader to think of a combat round this way:

[Combatants] are constantly side-stepping, twisting, and ducking, to avoid attacks or assume more favourable combat positions.

And then, when your opponent suddenly flees without carefully disengaging, you can just straight up stab at them because they just gave you a golden opportunity for no effort on your part.

As for the strolling NPC, that's legal in Rogue Trader, apparently as a design choice. The only way you get your "opportunity attack" against a moving target that hasn't used Disengage is if they were already engaged in melee with you, and becoming engaged due to moving only happens when the movement ends adjacent to an opponent (Move p. 241; Engaged in Melee p. 247). Since they're not stopping, they're not engaged, and you don't get the free attack. (Contrast this with another system that uses the "Disengage" design for "opportunity attacks": in early D&D, you become engaged immediately upon becoming adjacent, making opponents "sticky" and enabling them to control their adjacent squares by forcing a Disengage to move again.)

Why that's legal is an aesthetic design choice, as far as I can see. You can rationalise it with a story, or you can object to it on tactical design grounds — but regardless it's RAW. The easiest rationalisation is that opponents who aren't anticipating the need to physically stop someone are unable to do so — they're busy with whatever else they decided to do that round and the opponent ducks and weaves through the battlefield to wherever they're going.

The tactical objection is that this makes it hard to control the battlefield! That's reasonable, but the intuition is likely conditioned by Pathfinder's (unrealistic but functional) way of managing battlefield control.

To accomplish movement control in Rogue Trader, instead of it happening passively as in Pathfinder, you have to use a mix of passive and active tactics. Passively, you can either completely block passage by standing shoulder-to-shoulder, providing no space for an opponent to move through; or you can spread your forces out such that their movement has to end adjacent to one of you. Of course, that passive kind requires a lot of bodies and coordination. Active prevention can be done more solo but with more effort investment, by anticipating the need to stop an advance — which is what the story above implies is the solution — and using the Delay action to attack the incoming opponent. Because attacking someone immediately makes them engaged in melee, they won't be able to continue their movement after your delayed attack, and will furthermore be forced to use Disengage later to continue toward their position objective.