Rounded cakes always drove me nuts. They never seemed to be perfectly round like I wanted, like a ball. It was so annoying trying to figure it out! I always wondered why they never made a cake pan in this size? Not the small size Wilton makes, I was looking for a large ball. I finally figured out what I could do. Just use a rounded bottom mixing bowl!
I prefer a heavier steel ball. I pour the batter in just like I would a cake pan and bake. I will do this twice if I want a completely round ball or just once for a half ball.
After, I let my cake cool I trim off the top or bottom (depending how you look at it) to make a flat surface. Once I do this I crumb coat each flat surface and dowel one side of the ball. I do this so the ball does not come apart. Then I crumb coat the whole cake. I have had really good success using a crusting buttercream. This way if your ball is a little uneven you can just add my buttercream there and round it up a bit. From here, I would cover with fondant or more buttercream.
This technique works well for making any type of sports ball, hats, or helmets.