1. History of the game: If you really want to learn a lot about the history of rugby, click here for the Wikipedia article. However, most ruggers (aka - rugby players) will tell you that it all started with William Webb Ellis. At Rugby School in England, there is a stone that "commemorates William Webb Ellis who, with a fine disregard for the rules of football as played in his time, first took the ball in his arms and ran with it, thus originating the distinctive feature of the rugby game." This supposedly happened in 1823.
2. "Varieties" of rugby: The "regular" game of rugby is actually Rugby Union. However, there is Rugby League, which has a slightly different set of rules. There is also 7's Rugby, which is a much shorter game (7 minute halves) played with fewer players (7 on each team). You will also occasionally find 10's rugby, although Shawn tells me that it's typically reserved for social tournaments. The rest of this list is referring to rugby union.
3. The playing field: First of all, in rugby, it's called a "pitch." (That's actually the same for soccer, too.) From goal line to goal line, the pitch must be no more than 100 meters. The width needs to be no more than 70 meters. The goal posts (similar to American football) are 5.6 meters wide, and the bar is 3 meters above the ground.
4. Scoring: Think of a touchdown in football. It's the same basic concept here, except that the player who is in control of the ball must literally touch it down in the "try zone" in order to score. This is called a "try," and it's worth 5 points.
5. Points After Try: When a try is scored, the team gets to kick for extra points. However, unlike football, the ball is not automatically placed in front of the goal posts. The ball placement is determined by the location of the try. If the kick is good, it is worth 2 points.
6. Penalty Kicks: Sometimes, when a team commits a penalty, the other team is awarded a penalty kick. This is basically like a field goal in American football, and it is worth 3 points if it's good.
7. Positions and Numbers: There are 15 players for each team on the field during play. Each player wears a jersey with a number that corresponds to the position that he is playing. #1 - Prop; #2 - Hooker; #3 - Prop; #4 and #5 - Lock; #6 and #7 - Flanker; #8 - Number 8 (brilliant, isn't it?); #9 - Scrum half; #10 - Fly half; #11 - Wing; #12 and #13 - Center; #14 - Wing; #15 - Fullback. This shows how the players typically line up for a scrum. 8. Game length: A typically game is played in two, 40-minute halves. The game clock really doesn't stop running, with the rare exception of a very serious injury that needs to be attended to. The play itself only stops when the ball goes out of bounds, or if a penalty is committed.
9. Scrum: When the play stops because of a penalty, a scrum usually takes place. This is where the "pack" (#1-#8) of each team creates a fairly solid huddle. The packs then crouch down and at the signal from the ref, the front row of each pack begins to use their head/neck/shoulders to push on the other team's pack. The ball is put into the scrum from the side, and the players use their feet to get possession of the ball and then pass it back towards the rest of their teammates. This explains why Shawn (who plays in the front row) has had stitches across his eyebrows more than once. This is a scrum.
10. Lineout: If the ball goes out of bounds, a scrum is not used to restart play. Instead, there is a lineout. It's complicated, but basically, the team who should get the ball has a player throw the ball back in bounds. However, either team can catch the ball and retain possession. So, the teams line up parrallel with each other. When the ball is thrown (ideally, rather high in the air), the teams will lift a player (or two, depending on strategy) so that he can catch it. This is a lineout.
11. Moving the ball forward: A player can hold the ball and run with it. A player can also choose to kick the ball forward. However, a player cannot pass the ball forward. At any time, he can choose to pass the ball to a teammate. This is perfectly legal, as long as the ball is thrown behind him. Oh, and if he drops the ball, he can pick it up again, as long as the ball didn't go forward when it bounced. If that happens, it's called a knock on, and there will be a scrum (with the other team putting the ball in).
12. Being tackled: If the player is tackled, the play does not stop. The other team, of course, would like to take the ball from him and run. However, the player is allowed one motion after being tackled, and if he's smart, he'll use that motion to place the ball behind him...close to his team, and away from the other team. This is when a ruck typically takes place...but frankly, it's hard to explain and this thing is too long already. :)
13. Uniforms and protection: A rugby player will wear his team's jersey, rugby shorts (typically rather short, frankly), socks pulled up to his knees (and usually tied to stay in place), and rugby cleats. For the most part, that's it. Unlike American football, ruggers don't wear pads. Occasionally, some of the players will wear very thin protective padding on their shoulders/chests. A few players (normally the locks) will wear a scrum cap, which has a slight bit of padding...but this is to protect their ears in a scrum. It's definitely not a helmet.
So there you go! Everything you need to know in order to watch and understand the game of rugby....or at least, it's enough to get you started. :)