I'm currently preparing a Call of Cthulhu (6th edition, core rulebook) adventure. After having played a practice CoC session some time ago, and studied the rules, I found myself uncertain of how to handle rolls that will apply to all the investigators at once.
Here's an example, directly from play: A certain man is having a meeting inside a house with a mi-go. The house is on top of a hill, the two of them aren't on the lookout. The investigators decide to run up the hill to be able to hide beneath the windows, and I rule that a luck roll will decide if the man and mi-go happen to be looking through the right window when that happens…
But whose luck do I roll? If I asked each investigator to roll individually, the odds that they all succeed are drastically reduced. And since it takes for only one of them to fail for them to be seen, it seems unfair. So who rolls instead? Do I ask a roll from the one who is leading up the hill? From the one with the highest luck? Lowest luck? Do I decide instead that the man inside the house rolls luck to see if he looks at the window at the right time?
I'm also having similar difficulties with the use of hide skills. Hiding seems essential in some situations. Yet if a party of just four investigators hide together in say, some bushes, à la Shadow over Innsmouth, they are virtually doomed to be found if I ask for four individual rolls. And that is even if they all have great hide skills. Four investigators with 70% in hide each would only have 24% chance of success! Is that how it should be handled, or, once again, should I ask for the highest or lowest roll only?
Best Answer
With reference to Luck rolls (based on Call of Cthulhu 7th Edition rules, which the authors intentionally wrote as compatible with all previous editions), the relevant ruling lies on p90 of the Keeper's Rulebook:
Regarding other skills, assistance or coordination work differently depending on the situation. So, more than one character delivering First Aid allows everyone to make a roll with success granted to whoever happens to succeed (p88).
More generally - and in reference to your question specifically - the same principle as Group Luck rolls should apply to Group Skill rolls. The player with the character possessing the lowest skill should make the roll.
In both instances, these rules appear in 7th Edition, but not necessarily earlier. However, that means they're entirely suited to reverse engineer into earlier iterations of the system (given the same general baseline mechanics).