Adjust oven rack to center of oven. Heat to 325 degrees. Line muffin pans with baking cups; set aside. In a medium bowl, sift together flour, baking powder, salt, and baking soda; set aside.
In the bowl of a heavy-duty electric mixer fitted with the paddle attachment, beat the butter and sugar on medium speed until light and fluffy, 3 to 5 minutes. With mixer running, add eggs and vanilla extract; beat until combined.
With mixer on low speed, add 1 cup reserved flour mixture; mix until combined. Add 1/2 cup buttermilk; combine. Alternate adding flour mixture and buttermilk, ending with flour, until each has been entirely incorporated.
Divide batter evenly between baking cups. Bake until light-golden brown and a cake tester inserted into middle comes out clean, 25 to 30 minutes. Rotate pans halfway through baking. Transfer pans to a wire rack to cool.
Frost cupcakes with frosting. Immediately after frosting cupcakes, lightly press the edge of a 4-inch-diameter bowl into frosting to mark one curve on each side.
Using the curves as a guide, decorate cupcakes by placing licorice pieces on top of marked curves to form arced V shapes that simulate the stitching on a baseball.