The Rubber Ball is an item found by Harry Mason in Silent Hill. The pink ball is in the first floor storeroom of the Otherworld Midwich Elementary School. Harry must use it to plug up one of the drainage pipes on the school roof before turning the water pipe. Doing so makes the water flow to a farther drainage pipe, where the classroom key to the 2F northwestern room is stuck.
This is an example of an item being used for something other than its intended purpose, a trait which Silent Hill is known for.