Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a large bowl, whisk together flour, sugar, cocoa, baking powder, baking soda, and salt.

Add buttermilk, oil, eggs, and vanilla to the dry ingredients. Beat with an electric mixer on medium speed for 2 minutes.

Gradually add hot water to the batter, mixing until just combined. Batter will be thin.

Pour batter evenly into prepared pans. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.

Let cakes cool in pans for 10 minutes before inverting onto a wire rack to cool completely.

In a large bowl, beat butter with an electric mixer until light and fluffy.

Gradually add powdered sugar, beating until combined. Add milk and vanilla extract and beat until smooth and creamy.

Place one cake layer on a serving plate. Spread with a generous layer of frosting. Top with the second cake layer and frost the top and sides of the cake.

Decorate with sports-themed decorations as desired.