Preheat the oven to 350 F. In a bowl, combine the pineapple, sugar, flour and cheese; stir until well mixed, then spoon into a greased 9x13-inch casserole dish. Layer evenly with cracker crumbs and drizzle with the melted butter.
Bake for 20 to 25 minutes or until the top is golden brown and the mixture is bubbly. Remove from the oven and let stand for 10 minutes before serving.