The Quaffle is one of the balls used in the wizard's sport Quidditch. It is bright red and enchanted to fall slowly, so Chasers can easily catch it. It is also enchanted with a "Gripping Charm", so that it can easily be held by chasers and keepers.
From the Story
"The Quaffle is a bright, red ball the size of a football, which Chasers throw through the opposing team’s goalposts to score points during Quidditch."