I would recommend using a Betty Crocker Fill Pan, or something similar. It is shaped as a half-sphere, which you could then ice with white icing, and the black stitches to make it look like a baseball.
In order to make a cake that looks like a baseball you can go two routes. First you just use a standard 8 inch round and decorate the top to look like a baseball. Second you can buy a special pan from Wilton to make a ball cake.
To make that type of cake you need to find a baseball shaped cake pan .Mix the regular cake mix as directed.While you mix the cake mix make sure you pre-heat the oven to 350 degrees.make sure the cake is fully cooked before removing the cake from the oven cool and serve