First, let me assume you're running a tactical fantasy RPG such as D&D or Pathfinder. This particular advice solves a problem that D&D (especially 3rd-5th edition) and Pathfinder both have; but it sometimes crops up in other RPGs.
Calling the Fight
People fight for a reason, and they stop fighting when they achieve their purpose.
Most of the time, combat in your RPG should not be a "kill or be killed" fight to the death against desperate monsters who only want to kill the PCs, and are willing to die to do so. Start by figuring out what the enemy wants. Then give the PCs something they want badly enough to risk their lives for it.
The first encounter in the module Reavers of Harkenwold happens when the PCs, venturing into the valley to investigate troubling rumors, come across some soldiers assaulting the farmhouse of a holdout against their tyrannical overthrow of the local Baron. The dramatic question here is "Can the PCs stop thugs from murdering an innocent farmer?" Since they're heroes or at least mercenaries on a mission to stop these soldiers, it's worth getting in harm's way to fight them. They'll fight them, but they don't necessarily have to kill them all. And the thugs' goal is to put a stop to this rebellious farmer and make an example for others. Not "kill everyone who shows up."
|From Reavers of Harkenwold.|
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You've seen this scene in every high school movie. The bully slams the nerd up against the locker and threatens him. A fist is raised. The nerd is about to get it. The principal comes by, and the bully playfully scuffs the nerd's hair. "Oh hey Mr. Smith! uh... We was just playin'!" And the bully walks off before Mr. Smith can give him detention.
That's how you want this to play out. These Iron Circle goons don't even know who the PCs are at this point. They may be loyal, but they weren't ordered to fight strangers to the death. Once they put the torch to the farmhouse, they're done. If they can put some crossbow bolts through pesky interlopers, all the better! If those interlopers turn out to be dangerous adventurers, they'll run off shouting villain stuff like, "You haven't seen the last of us!" and "You'll rue the day you crossed the Iron Circle!"
When you write a combat encounter, the most important parts are not the terrain or the monster stats. The most important parts are why the encounter starts and what can end it. You also need to telegraph this to the players. Consider a low level Pathfinder encounter with five dire rats. Typically, you'd draw a dungeon, then decide one area was connected to a sewer, then put dire rats there, then choose how many based on the Challenge Rating math. You're not done! You need three more things:
- Why does this encounter start? The dark magic in this dungeon has mutated its rats. When the mutant rats see prey -- even something as large as human adventurers -- they attack.
- What can end this encounter? Individually, each rat will flee if it takes any damage at all. All of the other rats will flee once two of them have been defeated.
- How can the players know this? With a successful monster knowledge check with Knowledge (nature), a character knows dire rats are cowardly and will flee if they get hurt or if a few of them get killed.
The end condition (#2) actually makes the fight a little easier for the PCs. So you might adjust the Challenge Rating down to 1.
Common Objections and Hurdles
But in D&D or Pathfinder, some encounters exist to wear away the PCs' resources! While this is true, the players will stop using up their characters' best resources once the players have realized that they're going to win. If you've got two Cone of Cold spells left today, you're not going to use one of them to clean up the last wounded hill giant. You're going to save it for when you're facing down three more hill giants at full strength.
Yeah, but hit points are a resource too. That is true. But the PCs have so many healing magic options - even at level 1 - that this isn't an issue. And what if it was enough to be an issue? Is playing the fight out round by unnecessary round really worth it just to force them to camp for the night? No! You don't want either of those things to happen, if you can help it!
Anything can happen. Why not play to find out? In practice, this is not true. It is possible for the players to roll natural 1s for the next half hour, technically, but it is extremely unlikely. What are you fighting on for? Are you hoping some other GM will send reinforcements? Are you just playing out an extra quarter hour of combat to see if one of your monsters crits a PC?
It's clear the PCs are going to win from round 1! Where do you draw the line? This is a good question. There are different answers for the different layers of what's going on. First, from a game standpoint, your monsters are here to do something cool and scary. Those dire rats can give you filth fever! Once they've done it or failed to do it, you're closer to calling the fight. Second, from a story perspective, you need to answer the dramatic question. Did the PCs stop the Iron Circle goons from burning down the farmhouse and prove they're no pushovers? Time for them to flee. Third, there's an information disparity. The players don't know the stats of dire rats. Even the most experienced still can't remember everything, and you might have changed something. If you play and GM, you may have a better feel for this phenomenon: Because of that information disparity, the GM always knows the fight is over before the players do. You need to use your intuition to determine when the players realize they've won. You may call a few fights too soon (or too late), but you'll get the hang of it quickly. Watch for cues like players telling each other not to use their best resources or not to take reckless risks.
Why should my players let them flee? They might assume that if the Iron Circle goons run off, they'll have a harder fight later, with the extra goons. But in theory and in practice that's not likely to happen. First, in theory, if you're a tyrannical dictator sort, and your minions fail to intimidate a simple farmer, they'll be mucking stables for a month -- and that's if you happen to be in a good mood today. Second, in practical GM terms, it's a pain to rebuild tactical encounters on the fly to include the cowards from that last fight. Third, in practical "GM skill" terms, if you punish your players every time they do something that helps you maintain the excitement at the game table, you're shooting yourself in the foot. Stop it.
What do I do if my players still chase the fleeing enemy? You narrate the end. If the PCs are intent on slaughtering their fleeing foes -- shooting them in the back and such -- that's fine. Don't play it out round by round. Narrate it like this: "When they realize that they're outmatched, the Iron Circle soldiers break and begin to flee. Their commander shouts, 'They've got a wizard! Every man for himself!'" Player response: "We can't let them get away! I shoot the commander!" GM: "Do you plan to slaughter them all?" [Players all nod] "OK, you shoot the commander through the throat and he falls dead. The others try to flee, but you run them down, shoot them in the back, and make widows of their wives."
...Or you can give them a reason not to. Narrate it like this: "When they realize that they're outmatched, the Iron Circle soldiers break and begin to flee. Their commander shouts, 'They've got a wizard! Every man for himself!' Meanwhile, you notice that a small fire is smoldering in the farmhouse." This changes the focus of the scene from tactics to ethics. Do you shoot fleeing foes in the back? If not, what do you shout at them as they flee? If so, what sort of consequences might there be? Do you leave the farmer to put out the fire herself for a few crucial rounds or do you help her immediately?
What about hit and run enemies? The PCs are almost always a guerrilla force attacking a larger enemy organization. If the antagonists are also a guerrilla force, they might intentionally try hit-and-run tactics - but in that case, they will break off the fight before it's clear that the PCs have won. That's the point. You hit once and run.
What if the enemy is mindless, fanatical, or unable to flee? If it's clear that the enemy is defeated, but for some reason it can't or won't stop fighting, you have two good choices. One good option is to reduce it to 1 hit point as soon as you realize this, and don't even roll its saving throws -- have it automatically fail them all. Let the next attack kill it. This isn't cheating or fudging any rolls. Hit points are an abstraction. Your other good option is to narrate the rest of the fight: "There are only three zombies left. They keep coming, but you cut them down like cord wood."