Oliver Wood explains Quidditch:
"Right, now Quidditch is easy enough to understand, even if it's not too easy to play. There are seven players on each side. Three of them are called Chasers. This ball's called the Quaffle. The Chasers throw the Quaffle to each other and try and get it through one of the hoops to score a goal. Ten points every time the Quaffle goes through one of the hoops. Follow me? Now there's another player on each side, who's called the Keeper - I'm the Keeper for Gryffindor. I have to fly around our hoops and stop the other team from scoring. I'm going to show you what the Bludgers do. The Bludgers rocket around, trying to knock players off their brooms. That's why you have two beaters on each team - the Weasley twins are ours - it's their job to protect their side from the Bludgers and try and knock them toward the other team. Now, the last member of the team is the Seeker. This is the Golden Snitch, and it's the most important ball of the lot. It's very hard to catch because it's so fast and difficult to see. It's the Seeker's job to catch it. You've got to weave in and out of the Chasers, Beaters, Bludgers, and Quaffle to get it before the other team's Seeker, because whichever Seeker catches the Snitch wins his team an extra hundred and fifty points, so they nearly always win."