I'm making a 12x12 cake with a 1/2 soccer ball on top ... the ball is like 3" in diameter .. do I need to put support to hold up the ball?

If you're only using a half of the ball and it's only 3" I don't think you need a support dowel but I would use a dowel down the center of it to make sure it doesn't shift,

I would definitely put a board under it atleast...you never know what might sink and what might not.

I have done that in the past and have put a board under it. That was mainly since the ball was a different flavor cake and it was easier to cut that way. Something that size won't sink in if that's what you're worried about though.

cool .... I think I'll put the board ..better safe than sorry ...thanks for the reply