Reactions have lots of different triggers. Sometimes there's "degrees" of reaction. I.e. in 2HW's system you toss 2D6 vs a target number. Thus you can have a "great" reaction (2 pass), a "OK" one (1 pass) or a "bad" one (both fail).
In this post I noted the different elements of a reaction.
However I'd like to divide reactions into different types.
"Defensive" or "natural" reactions. These are reactions that would occur naturally, without much thought and require no special orders. They are usually unlimited.
Example: A unit comes under fire. It would be natural (and require no special orders from the commander) for them to fall back, or scatter into cover.
A defensive or passive reaction is anything that requires minimal training and comes naturally.
I.e I throw a ball at your head, you duck/put out your arm to deflect it.
"Aggressive" or "unnatural" reactions. These are reactions that you would have to be trained or ordered to do. This would not be the natural reaction of the average Joe Blo. They are limited.
Example: A unit comes under fire. They calmly stand their ground, reloading their crossbows with arrows whizzing around them. Or perhaps they charge the shooters, into the face of a hail of fire.
A offensive reaction is something that would require forethought, training or an express instruction.
I.e. I throw a ball at your head, and you actually head it back, soccer style. That's not an instinctive response, but one my soccer students would do.
Why two different types? It's useful for toning down reactions. It also prevents the "reacting" side to take too many offensive or aggressive reactions. I mean, "reacting" should allow you to interfere with the enemy, but the active side with the initiative (or the "move") should actually have an advantage.
Well, natural reactions occur for free. There is no "cost" or special roll needed. They are unlimited. The sergeant doesn't have to tell his troops to hit the dirt when the Mg42 rakes their position. They'll just do it! They don't need to pass any special tests to do it - common sense applies.
Aggressive reactions are not free. You may have to pass a morale test, or perhaps forfeit your next activation. You won't always be able to perform them - they are limited. If the sergeant wanted the troops to rush the MG42, he WOULD have to issue an order - it's unlikely they would all run into a hail of gunfire "naturally." Perhaps they would fail a morale test and not even do it at all.
Okay, how would this play out?
In the context of my Mordhiem-Infinity theoretical game, here's how it might look. Each unit uses an "Action Point" to activate in its active turn, from a common pool.
Two things trigger a reaction -
(a) if a unit is fired at
(b) if an enemy unit moves/activates within 12"
There are a few reactions to these -
Defensive Reaction (free)
- move away from the firer/moving unit
Offensive Reaction (cost one Action Point)
- move anywhere, including towards the firer/moving unit (including counter-charging into melee)
- shoot back at the firer/moving unit
As you can see, actions that cause harm to the opposing side are rationed (by drawing action points from their own turn). Maybe they'll even need a dice roll to even attempt an offensive reaction (i.e. archers need to pass a Discipline test to fire on enemy troops charging them, or they naturally fall back). You could even make units react depending on their type - Impetuous troops must always try to aggressively move towards enemy troops, and Skirmishers would need to pass a test or fall back passively.
I've previously used a variant of this in my Delta Vector homebrew space rules.
Ships can always make a defensive reaction - i.e. fire back/dodge/deploy decoys when fired upon (i.e. respond to direct attacks). These reactions were essentially limitless.
However if the reactee wants to initiate an attack (the enemy was simply moving within weapons range), it was an offensive reaction and the ship must pass a Crew Check. A failure means no more offensive reactions could be made and the ship was limited to defensive reactions only for the rest of the turn. The offensive reactions were thus limited/linked to crew skill.
There's Nothing New Under the Sun
I'm sure this has been done before, but I don't think I've seen it articulated distinctly which is why I've explored this in a bit more depth. Since reactions are actually an aspect of initiative/activation they impact in a significant way and are quite a broad topic.
Why divide reactions into different types? It helps tone down the impact of reactions.
The reacting (non-active) side can still move our of the way/avoid/respond to incoming fire, but it can't dominate the active side - the one with the initiative. One of the charges against reaction systems is that they encourage camping/passivity and this is one way to address this. Units can still take steps to preserve themselves, but if they want to blast an active unit across the map, it's gonna cost them.