All three of the U.S. military academies (West Point, Naval Academy and the Air Force Academy) have Rugby teams (15's & Seven's).  Rugby first appeared in the 1830's at the Rugby School in England. It was the genus for American Football. Rugby Teams have 15 players per team. Professional Rugby (International) is seen on TV more often than it used to be.
You can see a few new trends; aside from much better team work and tackling, the main one is using the Pop Kick as a means of moving the ball forward (passing the ball forward, as allowed in American Football, is illegal in Rugby) in addition to running with the ball. In any Rugby game, ball movement normally occurs from a player runs with the ball, laterals the ball to a teammate and (as mentioned above) pop kicks the ball in the air and runs under it and catches it, or a teammate does so; all while competing with the opponent for the ball.  

Seven's (7's) Rugby is a subset of regular Rugby. 7's games are played on the same field and follow the same rules (7's Rugby, as the name implies, has 7 players per team whereas regular Rugby has 15 players). 7's Teams are usually a subset of their affiliated 15's team(s); or in the case of Rugby Clubs, there may be multiple teams per Club aka RFC (Rugby Football Club). 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.
The 7's players are usually the more 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. 7's  games are played in two 7 minutes halves; whereas regular Rugby games are two 40-minute halves with 15 players per team.. 

Some basics you need to know to better understand Rugby are as follows:
- Rugby players are not usual as pretty as Soccer players; but Rugby players are always tougher and stronger than soccer players
- Rugby Players wear no heavy duty padding or no helmets
- 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 play stops; does NOT stop after a tackle; does NOT stop when the ball goes out of bounds; does NOT stop if 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",  (one Hooker, two Props, two 2nd Row, two Wing Forwards and one Lock (#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 (#9)
- In Seven's, it is a 3-person Scrum , 3 Running Backs and a Scrum Half (#9)
- 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 main on-the-field 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 MAJOR Rugby game on the planet is the Rugby World Cup which is played once every 4 years.
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