I've been reading the Quick Primer for Old School Gaming and I
have found it enlightening, to say the least. One of the issues it brings up is the use of skill checks to determine whether or not somebody does something "successfully." Instead, it suggests that the players describe exactly what they do in order to achieve a desired result, such as searching for a trap.
How should I deal with "skill" based challenges in a viable way? For example, somebody wants to leap onto the ground and somersault to avoid fall damage. Or another player wishes to slide down a bannister into a group of unsuspecting monsters, sword at ready.
These sorts of things would require some skill, and could possibly end badly. The guide mentioned a "to-hit" roll being of possible use, and also percentages. Could these methods be briefly explained? Are there other methods available?
Apologies for my lack of knowledge, just getting my feet wet with AD&D 1e.
Best Answer
I touched on this in your broader question, in that basically much of it comes down to two options:
If the action isn't something critical to the storyline or something entertainingly done (e.g. your example of trying to avoid fall damage) you would simply decide for yourself what the chances are of accomplishing the task, and roll (or have the player roll) percentile dice. (Though in the case of your example, I'd also assign a definite chance of failure which causes extra problems, so that players know there's a risk to going outside the rules.)
If it's something critical (i.e. "if we don't convince these people to help, our plans grind to a halt") or something entertaining (like your bannister example), you can simply rule success (in the latter example, perhaps a higher chance of achieving surprise, or if you're feeling generous an automatic one).
This really comes down to style and whatever your particular value of "common sense" happens to be; it's also possible to entertain suggestions from the players as to what they think their chances might be, and make up your mind from there. With 1e, there are a lot of seat-of-the-pants judgement calls like that, and the idea is to both keep the game flowing and to encourage creative thinking on the part of the players without simply giving them everything. This is one thing very different from later iterations of D&D, which started to incorporate a greater number of rules to cover such things.
If you want some kind of rules, you can always base a number of these things on a relevant stat check...perhaps your person trying to tumble will need to roll vs. Dexterity. The roll itself can be varied according to difficulty...for instance, if you judge the task to be quite hard, perhaps they have to roll Dex or less on percentiles; for something hard but not extreme 2xDex, for something of middling difficulty 3xDex, and so on. (5xDex is equivalent to rolling on d20, BTW.) You can assign chances of disastrous failure as being anywhere from 10-33% of the failure range, according to your judgement of how likely a failed check is to end especially badly. For instance, if our tumbler has to roll 2xDex to succeed, and they have a 15 Dex, you might decide that their disaster range is equal to 20% of the failure range. The resulting d% roll could be something like 01-30 Success (less or no damage), 31-86 Normal failure (take normal falling damage), 87-00 Disaster (take 150% falling damage). It's also possible to assign "critical success" ranges for the chance of something going exceptionally well (perhaps on 01-09 the tumbler takes no damage, and 10-30 half damage). You just have to decide on what sorts of good and bad outcomes you want to allow for the attempt.
A "to-hit" type of roll would be more relevant if some type of targeting was involved...for instance, trying to throw a grapnel. If you're simply trying to get it to hook on a wall, you could pick a fairly easy AC (say, 7-10) and have the character make an attack roll (modified, if you like, by their Dex bonus for missile weapons). If they want to throw it through a particular window, something tougher to hit (say, AC 4) might be in order. If they're aiming for a small, high up window, you could declare the target as AC 0...or even lower, if it's a really hard shot. (In this case, multiple attempts would certainly be allowed...though the amount of noise might attract guards, so getting the task done quickly would be preferable!)
The idea, still, is to keep the game interesting and keep it moving. Give them a chance of success, come up with a reasonable penalty for failure (and try to be at least somewhat forgiving about it, unless a character is attempting something truly harebrained or risky), and let the dice fall where they may. Allow the players to describe mitigating factors or ways in which they will attempt to bolster their chance of success, and nudge the chances a little more in their favor if their ideas sound good. Be flexible, be creative, and have a sense of humor about it...and always remember that while the GM is in principle supposed to be neutral, it never hurts to root just a little for the PCs...after all, your adventure won't get very far without them.