In a medium-sized mixing bowl, combine sausage, egg, crushed crackers and sage. Separate the mixture into two balls.
Heat a skillet to a high heat and brown the sausage balls. Drain on paper towels. Transfer the balls to a container with a lid.
Combine ketchup, vinegar, brown sugar and soy sauce in a small pot. Stir while heating the sauce. Let the sauce come to a boil, then reduce the heat to simmer. Let the sauce simmer for 20 minutes before pouring the sauce over the balls.
Allow to cool, then cover the balls and sauce, and refrigerate overnight. Reheat before serving.