CLICK HERE to Download the Project zipped (50KB)
CLICK HERE to Download A frozen XSI model. (350K)
Explanation:
I used three steps in order to get the final ball.
Step 1:
I got a primitive NURB sphere, and modifyed it's start\end parameters to dimentions that looked about
right to the eye. Then I duplicated the object 5 more times (6 in total) and rotated each of them to create
a round sphere.
Now after I got them in the rough size, but in the RIGHT place, I selected them all together, and tweaked the Start\end parameters
until I got those "patches" covering a whole sphere, with no wholes. (see image below) They are called "BASE SPHERES"

Step 2:
I got a primitive NURB grid, and apllied a Buldge deformer to it and set it's amplitude to 0 , then I did a "Deform by Surface" of the grid
on one of the "BASE SPHERE", and made sure it fits exactly of the base sphere,
Now I Instanced the deformed grid 5 times, and rotated and placed the instances over the other Base spheres
(dont defrom by surface, it's already deforemd on the first sphere)
I opened up the MASTER GRID's buldge paramter , pinned it, and opened it's Deform-by-surface dialouge box.
I tweaked the Buldge Amplitude, and the Buldge Curve, and the Scaling of the Defom-by-surface deformer,
until I got all grids aligned properly "almost stitched" to each other (Because all the other SLAVE grids are instances,
I only tweak the MASTER GRID, and the instances are automatically updated) (see image below)

Step 3:
I selected the MASTER GRID and converted the NURBS grid to a polymesh, then slected middle row of polygons,
duplicated them, and extruded them a bit, then I selected the other two remaining rows, and did the same
(this was done in order to get the stitching style look) Now I selected all the side polygons and duplicated them once
to make the edges harder.. (it's all still there in the MASTER-POLYMESH history)
I instanced the polymesh 5 times, and reordered them in place again.
To make the ball smooth I upped the polymeshes Aprximation to 2, but now I had holes in the seams..
So because every thing is still instanced and "in realtion" to the previous steps, I selected the BASE SPHERES again,
and the MASTER GRID and modified the paramteres even more, while watching the Polymesh update.. until I made
the holes disappear :) (image below)

**QUICK FIX**
I noticed the middle stitch should be rounded and not straight.. so
I also added a second buldge deformer, on the middle tagged points of the MASTER-GRID
so you can tweak that parameter too, to go from a Wilson to Mikasa to a Spalding... (just kidding)
Here is the Straight ball

and the More Curvy one:
