There are three kinds of balls. This one's called the Quaffle.
6 seconds sound clip from the Harry Potter and the Sorcerer's Stone movie soundboard.
You can hear this line at 01:07:26 in the Blu-ray version of the movie.
Quote context
[...]
- It was standing on a trap door. Which means it wasn't there by accident. It's guarding something.
- She needs to sort out her priorities.
- There are three kinds of balls. This one's called the Quaffle.
- Now, the Chasers handle the Quaffle and try to put it through one of those three hoops.
- The Keeper, that's me, defends the hoops.
[...]