Quidditch is the most popular game in the wizarding world. It's easy to understand, harder to play. Game is played between two teams. Each team has seven players each on broomsticks using four balls. Players are: 3 chasers, 1 keeper, 1 seeker, and 2 beaters. The quaffle, two bludgers, and the golden snitch. Six goals, three goals each side stand on opposite ends of the field. The game begins by the referee releasing all four balls from the center circle.
The quaffle is enchanted to fall very slowly so players don't have to constantly dive down to get it. Only one quaffle is used per game when one of the chasers throws the quaffle though one of the goals, that's ten points. The keepers job is to be the goal tender.
Bludgers are used by the beaters. Bludgers are round balls made of iron. The beaters use them to throw at their opponents and knock their opponents off their brooms, like an airborne obstacle. They are described as being bewitched to fly without any visible means of propulsion, although they do retain inertia, which makes them unable to change speed or direction swiftly.
The seekers job is to find the golden snitch. The golden snitch is gold, about the size of a walnut, and enchanted to move incredibly fast. When the snitch is caught, it ends the game and when caught, worth 150 points. However the chasers job is still important. Remember Viktor Krum caught the snitch, but Ireland still won.
There are 700 ways to commit a foul in Quidditch but most of these are not open to the public since the Ministry of Magic believes the public will get ideas. It is rumored all 700 ways to commit a foul happened during the first Quidditch Cup. After a good game of Quidditch, go get yourself some butterbeer at The Three Broomsticks!