How to print a ball?

Try spliting the ball in half and gluing.

The problem with supports, is that bottom will look pretty rough, compared to the top. 

I second the splitting in 2 solution.

Well I always sand everything I print. The print from a printer is in no way supposed to be considered a finished product. You will always need some sort of post processing to make a product that is at a level of finished goods. But then again I print for business and not just personal use.

it is possible to print a ball/circular shape without splitting it, but does require slower speeds, and sometimes support material may be needed - depends on your printer and the material being used.

if you are using slic3r, uncheck "detect bridging perimeters" in the settings - this will slow it down for overhanging perimeters (it wants to speed up those kinds of perimeters if that is checked). You may also want to slow down the speeds in general, but try it and see how it goes.

Try mesh mixer's support generator. It does a great job but you still may have to use the slicers support for the first 5mm or so