All 3 of the U.S. military academies (West Point, Naval Academy and the Air Force Academy) have Rugby teams. Rugby first appeared in the 1830's at the Rugby School in England when a Soccer player, who (mid-game) got bored with the no scoring --- picked up the soccer ball and ran into the net, That got some attention and Rugby was born.
Much later, Rugby was the genus for American Football when an American citizen (from England), who did not know the rules of Rugby, started American Football. Followed later by a Rugby player throwing a forward pass that the referee (at the time) did not know was illegal --- thereafter the forward pass in American Football became legal.
Rugby Teams have 15 players per team --- 8 in the Scrum (aka Scrummies or Forwards) & 7 Backs. There is a version called "7's which have 3 in the Scrum and 4 Backs. Both versions play on the same field & follow the same rules. Regular Rugby games play two 40-minute halves; 7's games play two 7-minute halves.
In any Rugby game, after a kick-off, a scrum or a line-out, the ball can only be legally moved forward by a player:
  • running with the ball
  • kicking the ball forward
  • [NOTE: a forward pass is not legal; more and more often in today's Rugby, players are finding ways to advance the ball by kicking it forward. Then they run it down themselves; or a teammate does or catches it on the fly. The only rule here is that said teammate must be behind the kicker of the ball, when kicked.)
The rules of Rugby are meant to make the game as non-stop as possible. The clock does not stop after a score or when the ball goes out of bound. The clock only stops at half-time, at the end of the game, or if the referee on the pitch (field) stops it (which is rare). Stopping play does NOT stop the clock.
In a Rugby game, play only stops (other than at half-time or the end of the game) when 1 of 2 things happens: the ball goes out of bounds or the Referee stops play. Restarting play, other than after a kickoff that follows a score, happens in 1 of 2 ways: A Scrum or a Line-out.  
Scoring occurs by kicking the ball through the goal posts, or when a player touches the ball to the ground in the opponents Try Zone or touches the ball to either goal post there. HOWEVER if an opposing player(s) physically gets underneath the player with the ball, preventing the ball from touching the ground in the Try Zone, there is no score and a Scrum is called on the 5-yard line --- throw-in to the attacking side.
A Scrum is a means to restart the game after a penalty. The 8-person Scrum (called Scrummies or Forwards) form a triangle, in a crouched position, and who, while in a Scrum, physically oppose the opposition's Scrum. The Referee controls when the 2 scrums come together. A Scrum consists of 3 Forwards in front (2 Props & a Hooker) who bind with their arms over each other's shoulders/backs, two 2nd Row players behind them, 2 Flankers on either side or the 2nd Row and a Lock behind the 2nd row.
Each 2nd Row player inserts their head between the hips of whichever Prop they are behind and the Hooker; and push with their shoulders on the front row. The Lock puts his head between the hips of two 2nd Row players and pushes with his/her shoulders. The two Flankers attach to whichever 2nd Row player they are next to, and push with one shoulder. 
Then the Scrum-Half, of the team awarded the ball by the Referee, can roll the ball in between the two Scrums. The Scrummies must stay together in their triangular form (until the ball comes out) and fight for the ball with their feet. Any Scrummy can pick the ball up when it gets to the back of the Scrum, but usually the Scrum-Half takes it and laterals to the Fly-Half. 
The normal starting arrangement of the Backs, after the Scrum-Half (who is like the Quarterback), is to put 4 backs on the strong side, 1 back on the weak side and a full back, who acts like a Safety. The 4 backs position themselves in line which is on a slant (to assist laterals). They are: Fly-Half, Inside Centre, Outside Centre and strong side Winger. 
A Line-out is another means to restart the game when the ball goes out of bounds. In that case a player from the team awarded the ball, stands right on the side line and throws the ball (like a pass) between the 2 lines of Scrummies, who stand in 2 lines, 2' apart, perpendicular to the sideline. The Scrummies jump for the passed ball and whichever team gets it, starts their offense.

In some countries, there are Rugby Clubs aka RFCs (Rugby Football Clubs). In England, and probably in other countries, many RFCs own their field(s) which commonly has a club house with locker/shower facilities and a lounge with a bar, on the property. A RFC may have several teams and their players may, from time to time, get selected to play in International games on Select Teams.
The 7's players are usually the most athletic of their affiliated 15's team(s); those with quicker reaction times and tackling skills are much more important since there are fewer players on the field. If you know American Football, 7's players would most likely come from the likes of Linebackers, Defensive Backs, Tight Ends & Running Backs. 
The Referee considers advantage --- meaning that if a team commits a penalty, s/he will NOT call it and stop play if the opposing team gains an advantage.  If the opposing side does not gain an advantage from said penalty, the Referee later (up to a point) stops play and brings both teams back to the point where the penalty occurred to have a scrum with the ball being put in by the opposing teams Scrum Half. 
A Mark is like a "fair catch" in American Football whereas the opposing player, who is catching a kick indicates that he will be claiming a Mark, which (when caught) stops play, is allowed to kick the ball however s/he chooses.
The game does not stop when a player is injured unless the Referee determines that the injured player is in the way of play and stops play. Medical help will come on to the field to assist an injured player during play and play does not stop unless again the Referee stops it.

Some basics that will help you understand Rugby are:
- Rugby players are not usual as pretty as Soccer players; but Rugby players are always tougher and stronger
- Rugby Players wear no heavy duty padding or no hard helmets --- like American Football players wear
- This (above) is an answer to how do we reduce CTE in American Football --- no helmets 
- The ball can be advanced by running with it or kicking it
- Any player can run or kick the ball
- A forward pass, or any forward motion of the ball caused by a player (other than running with the ball or kicking it), is a penalty
- A Rugby field size is a little larger than an American football field
- Each player stays on the field for the entire game unless hurt or substituted out
- There are two 40-minute halves; however the actual end of a half , or of a game, is totally up to the Referee
- The Referee is the one and only official time keeper
- Therefore the half ends and the game ends when the Referee says so 
- There are no time-outs
- The clock does NOT stop when there is a scrum, when the ball goes out of bounds, after a score or, in some cases, when a player is injured
- The clock stops when the referee stops it; only the Referee can stop the clock
- Touching the ball to the ground in the in-goal area (aka end zone) is called a "Try"; it is worth 5 points
- The Kick after Try, if successful, is worth 2 points
- The Kick after Try must be kicked on any point that is on a line that is perpendicular to the point where the ball was touched down in the In-Goal area (aka End Zone)
- If the player with the ball crosses into the In-Goal area but is held up such that s/he cannot touch the ball to the ground; the referee will blow the whistle to stop play and call a scrum at the 5 yard line awarding the throw-in to the team that last had the ball
- A Drop Kick can be made any time during play; if successful is worth 3 points
- If play is stopped by the referee, it may be restarted by a Penalty Kick (PK) or a Scrum
- If the ball goes out of bounds, the game is restarted by a Line-out (the clock does not stop)
- A penalty is called if a runner with the ball, when tackled and is on the ground, does not release the ball
- An off-sides penalty occurs when a player on one team is in front of a teammate who kicks the ball and cannot get involved in the game until the kicker of the ball, or a teammate was behind the kicker, gets in front of the kicker
- Blocking is not allowed; if the referee sees it and calls it, s/he will award a PK for Obstruction
- All rugby players must be able to tackle
- A Scrum consists of 8 players, who are called "Scrummies" or "Forwards",  (1 Hooker, 2 Props, two 2nd Row, 2 Flankers and 1 Lock (aka #8)
- There are 6 Running Backs in regular Rugby (one Fly-Half, two Centers, two Wingers and one Fullback)
- The main ball handler in regular Rugby, or Seven's, is the Scum Half (aka #9)
- In Seven's, it is a 3-person Scrum , 3 Running Backs and a Scrum Half
- There is one main on-the-field Referee and two side referees (who run the sidelines); all 3 are involved in officiating the game. 
- In big games, if setup, there is a TV booth with cameras capable of showing replays
- The main Referee may, after stopping play, call on the TV booth to resolve any debatable play
- The one and only main on-the-field Referee is the only authority on the field; what s/he says, is what goes
- The one in-the-field-of-play Referee may consult with either of the two side Referees
- A Yellow card is for a bad infraction; the player carded is sent off the field for 10 minutes (in Seven's  it is 2 minutes)
- A Red card is for a very bad infraction; the player carded is out the rest of that game and may not play in the next game for his/her team
- Rugby is played in 103 countries on this planet
- Major League Rugby (MLR) brought professional Rugby to the U.S. for the first time in 2018
- There are international Rugby games; the big one is the Rugby World Cup
- International games are between countries
- For International games, each country can use any Rugby player who is a citizen of their country
- USA Rugby fields the USA Eagles to represent the U.S. in international games
- The USA Eagles use players from any other Rugby organization in the U.S. including the MLR
- Generally, the top Rugby teams on the planet are the All-Blacks (New Zealand), the Springboks (South Africa) and the Fiji National team.
- The most important Rugby game on the planet is the Rugby World Cup which is played once every 4 years.
Professional (paid players) in the U.S. & Canada play in the somewhat new organization called "Major League Rugby (MLR)". It consists of 9 teams (8 U.S. & 1 Canada). They have announced that 3 more teams (New England, Atlanta & Wash DC) will join the MLR in 2020. The local team is the Seattle Seawolves who are the defending 2018 MLR Champions.
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