Heat oven to 350°F. Lightly grease a 2-quart baking dish.
Drain pineapple very well and reserve 1/4 cup of the juice.
Whisk sugar, flour, salt, and pepper in a large bowl.
Stir in drained pineapple and the reserved juice until evenly coated.
Fold in most of the cheddar, saving a small handful for the top. Spread mixture in the dish.
Mix crushed crackers with melted butter until crumbs are evenly moistened.
Scatter the reserved cheddar over the casserole, then cover with the buttery crumbs.
Bake 28–35 minutes, until bubbling at the edges and the top is deep golden. Rest 10 minutes before serving.