Chill the watermelon balls and pineapple chunks until ready to serve.
In a large jug or pitcher, combine the orange juice, grapefruit juice, pineapple juice, and lemon juice.
Taste and add sugar as needed, depending on the sweetness of the juices.
Add water as needed if you want to mellow the citrus flavor.
Stir in a few dashes of Angostura bitters.
Cover and refrigerate for at least 1 hour, or until well chilled.
Add the chilled watermelon and pineapple just before serving.
Pour over ice and serve cold.