Make cake. Prepare batter following recipe directions. Bake and cool 1-layer cake, 3 in. high. Place cake on cake circle.
Ice cake. Prepare buttercream icing following recipe directions. Tint portions green and brown. Reserve remaining white. Use spatula and green icing to ice cake smooth.
Decorate cake. Use toothpick to mark a football shape, 4 in. x 2 in., on top of cake. Use white icing in cut decorating bag to pipe football-shaped mound within mark. Use tip 16, cut disposable decorating bag and brown icing to pipe stars on mound. Use tip 3, cut disposable decorating bag and white icing to pipe lines and laces. Use tip 233, cut disposable decorating bag and green icing to pipe grass around football. Use tip 3, cut disposable decorating bag and green icing to pipe bead bottom border.
The star tip creates the most celebrated, easily accomplished decorations! The serrated edges of the star tip make ridges in the icing as you squeeze it out. Because fill in requires so much piping from the same bag, keep replenishing icing in bag.