Prepare and bake cake mix according to package directions, using a greased 13x9-in. baking pan. Cool completely on a wire rack. Crumble cake into a large bowl. Add frosting and mix well. Shape into 1-1/2-in. balls. Place on baking sheets. Chill cake balls until firm, at least 2 hours in freezer or at least 3 hours in refrigerator.