The sport of quidditch was originally adapted from the Harry Potter series by students at Middlebury College in 2005. It has since grown as a sport, with many colleges and communities fielding teams from around the United States and the World. US Quidditch handles US based quidditch events, culminating in US Quidditch Cup in the spring. Teams must first compete within their respective regions to earn a bid to the World Cup where they have the chance to compete against teams from other regions. You can read more about the history at USQ's website.
A quidditch match consists of two teams of 7:
The game begins with both teams lined up kneeling down on their side of the pitch, looking down at the ground. The quaffle (a slightly deflated volleyball) and the three bludgers (slightly deflated dodgeballs) are lined up in the middle of the pitch. The referee will yell "Brooms Up" at which point the game begins with a mad dash to get the balls. After this point all players must keep a broom between their legs while they are in play. Failure to do so will result in the player being sent back to their hoops before they can re-enter play.
The bludger game:
The two beaters on each team attempt to throw their bludgers at the opposing team. When a beater from the opposing team hits a player, that player must then dismount their broom and run back to touch their hoops before they can reenter the play.
With the exception of the seekers, players may attempt to tackle players who interact with the same ball as them, as long as the other person is in possession of a ball. All tackles must be made from within the opposing players line of sight (including peripherals), with one hand, and the point of contact must be between the shoulders and legs. An exception to the tackling rules occurs when a keeper is within their own keeper zone (a 3 yard section of the field in front of their hoops that also extends infinitely behind the hoops): they cannot be tackled.
The quaffle game:
The three chasers and a keeper are commonly known as the quaffle players since they may only interact with the quaffle. Their goal is to get the quaffle through the opposing team's hoops, thereby scoring ten points. They must also prevent the opposing team from getting the quaffle through their hoops.
The snitch game:
The game changes once the snitch is on pitch. The snitch is released at 17 minutes, with seekers released at 18 going after the snitch. Depending on if the game is in snitch range (when the game is within 30 points) or out of snitch range (when a team is up by more than 30 points) determines a team's strategy. When the snitch is caught, the team that catches is awarded 30 points and the game comes to an end.
For a more in-depth look at the rules on USQ's website.