I tried my hand at GMing for the first time recently and my biggest challenge was figuring out rules on the fly. I frequently found players wanted to do things that I didn't know the rules for, forcing me to choose between stopping game play to look something up or shooting from the hip making a ruling that seemed reasonable and hoping I wasn't saying something that I might have to take back later.
To be clear, I am not looking for an "out" to not do my homework. Before my session, I read through the core rule books and the pre-generated module I was using. I printed off, highlighted, and made notes on the module, monsters, and "extras" (eg. spells, abilities, skills, etc.) that I anticipated being part of the session. I even mentally ran through all the sections with the pre-generated characters and looked up the rules for all the things I would have done in the module. However when game play began, for some reason my players did not follow my script (surprise, surprise). They used skills and combat maneuvers I wasn't expecting, so I hadn't brushed up on.
How do I keep flow and balance in the game when players want to do something and I don't know the rules?
Some things I can see being helpful (but not an exclusive list):
- Techniques to keep play alive while rules are being researched rather than "Everyone stare at the GM while they read".
- Rules of thumb that can help make good rulings without looking up rules.
- Better ways to prepare so I will be more likely know the rules when they come up.
For the record, in this session I was playing Pathfinder, but I am hoping for more general techniques that can be applied to many different systems. If I get comfortable GMing Pathfinder and decide to try out 5e, I would like to be able to use these techniques again when new rules I don't know come up.
Best Answer
Know the most common rules. I assume from your question that you are not making rulings about things like attack rolls and damage - but if you are, you shouldn't be. You actually need to know this stuff.
The players are responsible for their characters. If what they want to do is written on their sheet then they need to know what it does. If they don't know what it does then it doesn't do anything. Allowances can and should be made for inexperienced players.
Know when to look things up. There are rules you don't know and have no idea where to find them: those you make rulings on. There are rules you sort of know and could look up in 30 seconds: those you might choose to look up - or get someone else to look up while you deal with the next thing.
Understand the core mechanic. Most modern RPGs have a central core mechanic (older RPGs can be a hodge-podge of mechanics). For example, D&D from 3.0 on has "roll a d20 add modifiers compare to a target number" and FFG Star Wars "Roll a bundle of dice with strange and confusing symbols and try and divine what they mean by reading them like they were chicken entrails" (I actually like this game but that is its core mechanic). If you know the core mechanic you have a skeleton to hang your rulings off that means they will "fit" the game.
Determine how hard it is to do the task. Link it back to the rules you know - is it easier or harder than: hitting someone with a sword? casting a spell? running? jumping? Combine this with your core mechanic to determine what the character needs to do to succeed. For example, D&D 5e says this (DMG p. 238):
Make or buy a GM screen or cheat sheet. These list out the common rules and tables etc. - it's far easier to find these on a few sheets of paper than buried in an entire book - particularly if that book was laid out by Wizards of the Coast. Making them yourself is better because by the time you make them, you won't need them because the rules will be embedded in your skull. Here are some examples.
Rulings stand for the session. When you make a ruling, write it down. After the session look up the correct rules and decide if from this point forward, you will use your ruling or the "official" rules. Don't retcon things if you do decide to change.