Meats such as beef, pork, veal, lamb and poultry can be refrozen when they are still firm with ice crystals. Meat still safe to eat can be cooked and refrozen. Discard meats if any signs of spoilage are present. Fruits usually ferment when they start to spoil which will not make them dangerous to eat but will spoil the flavor. Defrosted fruits that smell and taste good can be refrozen.
Spoiled vegetables can be dangerous.
Shellfish, prepared foods or leftovers should not be refrozen if defrosted. If the condition of the food is poor or even questionable, get rid of it. It may be dangerous. You can cook and eat thawed food mixtures like casseroles, pot pies, dinners, or pizzas if you are certain they have not reached a temperature above 40 F for more than one to two days. Do not refreeze these foods.