Would I be best off starting with the offense and explaining the quarterback first, then the running backs and wide receivers? Keeping it simple with the explanation that almost every play is a run or a pass?
Another method would be to point out every position on the tv screen, but I am not sure a newbie needs to know about the difference between a guard and a tackle early on.
Start with running. Everything is built off of that.
A thread on this subject arises every year. My advice is to read through them, notice how quickly to topic descends into incomprehensible minutia. Keep it as simple as possible. The game is about advancing the ball towards the end zone. You get 4 tries to make it 10 yards, and if you do, you get 4 more tries for the next 10 yards. Success = 7 points (yes, I know it’s 6). Failure = turnover. Field goal = 3.
That is honestly all you need to tell them. There are a bunch of ways to advance the ball via running and passing the ball, but they honestly don’t need to know about the line of scrimmage. They sure as hell don’t need to know what a DB is or what left guard does versus a left tackle.
I’ll stick to the classic; " A Violent ground acquisition game which is in fact a crypto-fascist metaphor for nuclear war. 
I am an adult and not familiar with AF (European, you know…), but I thought it was all about the National Anthem at the start, the intermissions for the adds in between, the music performance at half time, specially during the Super Bowl. The rest, I was told, is accessorial.
I’ve heard it described as a simulation of warfare, in which you use rules and tactics to capture the opponent’s territory.
I had an epiphany a few years back: Football is trench warfare, hockey is Blitzkrieg. In football, you carefully set all your pieces into place, then go for the Big Push, and see what happens. In hockey, you keep everything in motion, looking for the opening to strike a winning blow; you’ve got a goal in mind, but how you get there is very fluid.
To whatever else I might tell them, I would link an article like this:
I would start with the simplest explanation, the one Sean Payton gave to the British press in London when the Saints were there: Try to get someone from your team, who has the ball, into the opposing team’s end zone. Failing that, then kick the ball for 3 points.
You can always use the old George Will line about football: that it combines the two worst aspects of American life — violence punctuated by committee meetings.
That’s a straightforward start!
If the adult is familiar with Rugby Union, then you can say it’s a version of that with some minor changes e.g.
There is also an enormous trivia game conducted between the ads.
I’d suggest starting from the premise that American/Canadian football is nothing like soccer, hockey, basketball, or any other sport that involves continuous, fluid movement, with on-the-fly decisions and actions. Rather, it is like a chess match.
One play, and the other team’s response, affects the next play and the other team’s response, and so on and so on. Like chess, sometimes the move takes a little while to figure out, which is why play stoppages happen, though within a prescribed time limit before the game goes again. As such, the game doesn’t “flow,” like soccer, hockey, or basketball. It starts and stops, as it was designed to do. Also, like chess, it’s a game of strategy: “If we do this, and they respond that way, as we expect, we should be good. But what if they don’t? Can we salvage this somehow if they X, Y, and Z?” This is a game that requires brains as well as brawn.
The chess analogy is a good one, I have found, when dealing with friends from the UK and Europe, who try to equate soccer/hockey/basketball to American/Canadian football, because they’re used to sports where the action never stops (well, it does, but not as often as in football). But the chess analogy helps a lot: move, respond, assess field position, make a decision; move, respond, assess field position again, make a decision, and so on.
Once that’s understood, the rest should be easy: get the ball into the opponent’s end zone to score. Details as to how that is achieved can come later, but I have found that the chess analogy works well to explain to non-North Americans why our football is nothing like soccer or other free-flowing sports. Once they understand that, the details–scoring, player positions, player functions, etc.–can follow.
Yeah, the biggest differences between American football and superficially-similar sports like soccer is that football has discrete plays, that start and stop at marked, definite times; and that there’s a strong notion of “possession”, which usually doesn’t change in the middle of a play. And the notion of “possession” is so strong, that there are multiple separate teams within the team, with completely different players, to handle offense and defense.
I would start by explaining the field and yard lines, that one team will be on offense and in possession of the ball, and the other on team on defense. Then briefly explain possession will alternate between the teams and then starting with an offense on some yard line then go through some offensive plays that will advance the ball, leading to a punt to demonstrate how possession changes. Explain a some more offensive plays to advance the ball leading to a touchdown as an example of scoring.
Many of the other details go over the head of newcomers who don’t yet understand the basic pattern and flow of the game. I’m not sure if the details of the complex and arcane rules of football or baseball are the worst, but refs and umpires still have to confab on the field to figure out a ruling in many games.
You definitely need to explain downs before punts, or the obvious question is “why would any team ever punt?”. Also, if you’re watching a game with a group, a first down is the most common reason for fans to cheer, and you want to know why everyone’s cheering.
There are about 11 minutes of action in an AF game so peripheral entertainment is indeed critical. Fans must also have the patience to endure multiple lengthy periods of debate while the group of moderators determine the outcomes of plays.
OTOH it is an absurdly wonderful game upon which to gamble.
Here is a handy YouTube explanation of American football. It makes about as much sense to me as any other.
I remember the first time I went to a Cowboys game, I was not in the seats yet and I heard a raucous cheer. It was as if the Cowboys had just scored a touchdown. Turned out it was…just a first down.
Bumping an older thread but this is how I’d do it. My cousin immigrated from the Philippines and she asked me this very question, and this is how I did it. Start with 4 downs to get 10 yards. Keep it simple.
It’s best explained while watching a game, so do that.
● When a team gets the ball, no matter where they start from, they have to move it 10 yards. They get 4 attempts to get 10 yards. These attempts are called “downs”. If they get the 10 yards (or more), then from that position on the field they get another 4 downs to get another 10 yards — this is called “first and ten”, or, first down and ten yards to go for another first down. If they don’t move the ball 10 yards then the other team gets the ball.
● If they can keep moving the ball down the field and into the end zone, they get a touchdown worth 6 points. They also get one more play to get an extra point, or an extra two points — the team chooses which method to try for, either 1 or 2 points.
● If the team moves the ball down the field but they do not get into the end zone, but they get close enough, then they can try a field goal. If that kick is good they get 3 points.
● At any time during a team’s ball possession, that team can give up the ball to the other team. This is usually done with a punt, typically on fourth down when the team thinks it is too far for them to go to get the first down.
And that’s it. Keep it simple and basic. The rest can come later.