Preheat oven to 350°F. Line 24 muffin cups with paper liners.
Prepare cake according to directions. Divide batter evenly between prepared muffin cups, filling each cup 2/3 full.
Bake in preheated oven for 17-20 minutes, until a toothpick inserted in the center comes out clean. Remove to wire racks and cool completely.
Using a stand or hand-held mixer, beat butter on medium-high speed until light and fluffy, about 3 minutes. Gradually add icing sugar, milk or cream and vanilla extract, beating thoroughly. Taste and adjust as needed. Remove 3/4 cup of icing and set aside.
Add cocoa powder and chocolate extract, and mix thoroughly. Add more milk or cream if needed.
Place chocolate butter cream in a piping bag fitted with a star decorating tip. Starting at the top center of a cupcake, pipe in a zigzag pattern, gradually increasing until you are at the middle of the cupcake, and then decreasing until you reach the bottom center.
Place vanilla butter cream in a piping bag fitted with a small round decorating tip. Pipe one line vertically down the "football", and three smaller lines across horizontally to make the laces.