In a bowl, combine the milk , onion, crackers and season salt. Crumble beef over mixture and mix well. With wet hands, shape into 1 inch balls. In a large skillet over medium heat brown meatballs in small batches, turning often.
Remove with a slotted spoon and keep warm. Drain skillet.
Drain pineapple, reserving juice: set pineapple aside. Add enough water to juice to measure 1 cup. In a bowl, combine the cornstarch, pineapple juice mixture, vinegar,soy sauce, lemon juice and brown sugar until smooth. Add to skillet. Bring to a boil; cook and stir for 2 minutes or until thickened. Add the meatballs. Reduce the heat; cover and simmer for 15 minutes. Add the pineapple; heat through.