In order of necessary agility:
Seeker
Chaser (tie) Beater
Keeper
Yes, there is one Quidditch match in Harry Potter and the Philosopher's Stone for Xbox. However you only play the last few minutes of the match.
The seeker must catch the golden snitch.
Yes. After the first match of Quidditch in his sixth year.
Missed the snitch and flew into a wall
Professer Quirrell.
A dementor!
The Quidditch referee at Hogwarts is Madam Rolanda Hooch. During Harry Potter's first year, Severus Snape referred the Gryffindor v Slytherin match in an attempt to protect Harry as Quirrel had tried to kill him in the previous match. The referee for the 1994 Quidditch World Cup was Hassan Mostafa.
There are six players in a volleyball court during match.
After Harry's first flying lesson with Madam Hooch, Professor McGonagall took Harry to Oliver Wood, who was the one who first taught Harry how to play Quidditch.
A total of 22 players play at a time in a football match, 11 players in a team.
In Harry Potter and the Prisoner of Azkaban, Gryffindor (Harry's team) win the Quidditch Final.
There are six players on the court during a match.6