I'm hoping the pictures are clear enough that you can build the ball solely from them but I have included text on each step just incase you get stuck. If you can understand the step just by the picture then you're pretty awesome and should just ignore whatever I wrote.
A short video showing the roundness of the ball. More exciting video coming soon.
Step 1: Parts
I'm including a parts list of the parts I used in this Instructable so that it will be easier to understand. Of course you can always substitute for parts that you don't have with ones that you do (like using two 2x4s in place of the 4x4 or using two 2x4s in place of the 2x8) but just be cautious about maintaining structural integrity. I know rainbow warrior (using bricks in any and all colors) is sometimes the only option but the shape of the ball shows up better in solid color so if possible, try to stick to just one color.
-8 1x4 bricks with knobs
Step 8: Now do it 5 more times!
Flip over 4 side pieces. Attach the 1x4 bricks with knobs to the pieces. Make sure that the bricks with knobs are attached to the red pieces using their extra row of studs (not the ones that are on top of Lego bricks normally) so that the normal row of studs point outwards. Also make sure that two of red pieces have the bricks with knobs attached horizontally and that the other two are attached vertically.
Attach the third and fourth sides and you'll have basically a round box without a base or lid.
I think this red one would make a great clown nose for a giant Lego sculpture. What kind of uses can you think of? If you make a Lego ball with the help of this Instructable, I would love to see it posted in the comments.