According to the Legend Quest rule book:
Adventurers have a special “edge” that allows them to perform at their best in the worst of situations. Others, not as at ease with adventuring, will suffer for their lack of that “edge”. Any non-adventurer will be -20 on initiative, defense and sensing rolls. This is to simulate jumpiness, distractions and not always looking over one’s shoulder.
So is “adventuring” the only time this happens? No! A well used optional rule within the play-testing crew has been that this lack of an edge affects a wide range of environments where one might not be familiar. Here are some examples:
Sea Legs - Any land lubber on a boat would experience the same type of penalty. They wouldn’t know where to stand, how to avoid the ropes/sails, would be more unsteady on their feet, etc. Once they gained their sea legs, typically by being on the boat for a week or so, they would likely not suffer the penalty, even if they never fought during that initial period of time.
Mounts - There are already rules about mounted combat, but what about switching to a completely different mount? Put a skilled horseman on a flying pegasus, and he is going to suffer a penalty. Not only is the three dimensional form of combat likely to be new to him, but he is also going to have to look out for those massive wings. No use clipping your own stead’s wings while trying to stay in the air. The same would be true of a person riding a massive beast, such as a dragon or elephant for the first time. Without training, it would be incredibly difficult to balance on a back that you can no longer wrap your legs around.
Flying - On a similar front, someone who had never flown before (we’re assuming a flying spell or some other sort of individual magic here), would suffer the penalty. Imagine strapping on inline skates for the first time and then trying to conduct a sword fight. That’s what flying should be like.
Major Military Action - Skirmishes are one thing, but when you line up 10,000 soldiers of each side of the battlefield, fighting becomes a whole different thing. For those (and we mean adventurers here) who have not drilled in close order combat with large numbers of troops, simply being shoulder to shoulder with 10K of your closest buddies is going to throw you off your game. The comedy in my head right now is a guy with a flail standing in a line of pikemen. There was a reason that all those soldiers used spears, while adventurers often go for more exotic weapons - spear work great in close quarters. Anyway, not being use to that style of combat should put those folks at a disadvantage.
Underground - Similar to close quarters would be underground. Here it is likely the walls and ceiling that are going to hang you up instead of your buddies, but the effect is similar.
Let’s stop being so long winded and just hit some of the other environments: underwater, on the back of a giant sea turtle (you run your campaign your way, I’ll run mine my way), volcano/hell, a gravel (unsteady) path on the side of a mountain, amidst the trees (no, not on the ground - actually up in the tree limbs standing on branches), zero gravity, and the list just goes on and on.
Why do you do this? Well for two reasons - #1 - it makes sense. #2 - it can help you even the “playing field” against your heroes. Adventurers should be better suited to investigate a haunted coal mine then the local sheriff. (That’s a revenue maker for your players.) At the same time, the duke’s sentries should be better suited to take the field, than some dragon slayer. Oh, he’d still be a fearsome foe, but he’s out of his element. Quick example - A group of halflings live amongst the boulders on a steep mountain side. Not only have they adapted their defenses to take advantage of the difficult and often blocked pathways, but they have learned to fight and move like mountain goats. With these nimble warriors leaping from boulder to boulder while stabbing with their daggers, they should have an advantage over anyone who assaults their mountain home and fights, well, like a normal person. Think of it this way - How many American kung-fu movies have you seen where the American hero keeps getting kicked by the martial artists, because he doesn’t know how to defend himself. So he dodges for a short time and watches the speed demon attacking him, until finally, he reaches out and blocks the kick. OK, not the best analogy, but it is like that. Given time, they can get use to this environment and style of combat, but the first couple of times, they’re going to be like the new kid on the inline skates.