Combat Manoeuvres - Trip and Disarm

This post started life as an explanation of how I was at an impasse in developing a rule for combat manoeuvres, but the very act of writing it has fixed the issue.

If you beat the score needed to hit your opponent by 10 or more you get the opportunity to make a combat manoeuvre or take an extra dice on the kill roll.

The combat manoeuvre is resolved by opposed melee bonus + d6 (open).

Right from the start of developing Explore I recognised that some form of combat manoeuvres would be required, but as it wasn’t essential to playing the game, and needed to compliment the play style that would emerge from the other rules, I left it for future inspiration. Recently the lack of such rules has become more evident in play, particularly when facing a far inferior foe, so I started to work on it.

Too Much Choice?
Firstly I decided that this should be an option that presented itself occasionally in combat, rather than a choice that had to be made every round. That would typically be on a critical result, and in Explore the equivalent is your attack roll beating the target by 10 or more. Currently in that case you get an extra d10 for damage, which as a side-effect makes the counting up your to hit score interesting even when success is clear.

This leads us to the first half of the combat manoeuvres rule - if you beat your "to hit" by 10 or more then you get the opportunity to make a combat manoeuvre or take an extra dice on the kill roll. This brings home the fact that an attack roll is not a single swing of your sword but represents the best opportunity you get in a sequence of parries and feints. For example, you might swing your sword, it is parried, but you follow through with a thrust from the dagger in your offhand – that’s all counted as a single "attack".

What are the stats of this? It’s usually about an 8% chance (given that you succeeded), but if you have greater than 75% chance of a hit then this rises quickly – for example if you only need 3 to hit, then 36% of the time you get to use a combat manoeuvre. Thus a greater proportion of successes turn into combat manoeuvres against lesser opponents.

Making a Resolution
So how to resolve the combat manoeuvre? It would make sense for this to be a second 2d10 open roll (same as the attack and kill roll) – but would it be against their Melee or Parry? I don’t think a shield should give you a bonus, so it would be versus Melee. Would it include weapon bonuses? I think it should be easier to disarm someone if you're wielding a sword, so yes. Would it be opposed rolls or a fixed bonus? The arbitrary fixed bonus seems a bit, well, arbitrary. It can’t be the standard idea of an opposed roll (both sides roll 2d10) as that increases the variance of the result (increasing the factor that luck plays and reducing the importance of skill). The alternative is an opposed roll where both sides roll 1 dice – this keeps the numbers correct and seems appropriate.

Playing the Odds
So what’s the chance of winning here, compared to simply taking the kill roll? That is, if you hit by 10 is it better to take the extra dice on the kill roll or take the combat manoeuvre?

Consider two first level fighters with full armour with sword and shield. Parry:7, Attack: 4, Kill:4 Saves:11/14/17/20 (23). If you hit by 10 and take the extra dice, then with three dice the chance of getting an outright kill is 35% - fairly high.

Imagine much better combatants – P:12, A:9, K:9, 11/17/22/28 (33).  A kill would be rolling 24+ which is 12% chance. (Their combats typically last longer and have several wounds before a kill)

The better versus the worse opponent needs to roll 14+ to kill (70% chance), the worse versus the better needs to roll 29+ (4% chance).

So that goes to a table of 35% / 4% / 70% / 12%.
With a single opposed d10 roll system the chance of success are 45% / 11% / 84% / 45%.

This means the chance of disarming is higher than the kill, which I like, and I also like the fact that the chance between two equal opponents is always the same – but I want the other values to be more extreme. Skill should play a larger role here, and 70% chance of death should be swapped for near certain disarming.

Less is More
With a single opposed d6 roll system the tail end decay is the same but there’s a steeper curve in the middle so this gives us what we want – the chances of success are 42% / 5% / 94% / 42%.

Using d6 instead of d10 solves another problem I found in play testing when I tried out using single d10 rolls in another area of the game – players would invariable roll two dice instead of one and when told they should have only rolled one wanted to keep the higher number! It also highlights another issue I found when play testing open d6 – players don’t like to accept replacing a 6 with 2d6. In this case we can offer a choice to reroll if you like – thus if you lose you’ll always reroll but if you win you might still reroll for a great success.

Over Achieving
If beating by 10+ is good, we need a rule for beating by more:

If you succeed by 20+ in the attack and choose a combat manoeuvre you get two dice on the kill, or 2 dice for the combat manoeuvre.

In addition I’d like great success or failure at a manoeuvre to be rewarded. Beating by 10 isn’t very likely with the squeezed middle of the probability curve, so I’ve reduced it to beating by 5. This equates nicely to evenly matched opponents rolling a 1 and a 6.

You are almost guaranteed this if you far outclass your opponent, but only 11% of evenly matched successes are great successes. Unfortunately the curve for opposed rolls is less smooth so if you are outclassed 30% of your successes turn out to be a great success - but this is a compromise I’ll accept.
Great failure I’ll take to be failing by 5 or more.

Great Failure (lose by 5): Fumble! Opponent disarms you…
Fail: Nothing
Success: Disarm or Trip
Great Success (win by 5): Disarm (all weapons), grapple hold, can throw opponent if strong enough.

But what about?
This only covers trip and disarm - actual "manoevering" your opponent around the battlefield is next to come...