Drawing spheres in a realistic manner, with appropriate shading, is always a challenge and doubly so when they have a smooth surface. However they are an excellent technical challenge and a good pointer as to whether your shading is up to scratch. So today I picked up my son's football and placed it with a decent source of light:
Just looking that the photo it's clear that the ball doesn't exactly have a visible edge; the surface just curves away until you can't see it any more. However the stitching very clearly indicates how the surface bends and so I decided that these would be my key elements. Firstly I roughly shaded in the whole shape - making sure to draw roughly in line with the surface but also to cross-shade in order to smooth the texture. Then I moved onto drawing in the lines of stitching and appearance of the individual panels:
The main factor here, I found, was that no matter how much shading I added to the right-hand side of the ball it never seemed to be enough! So most of my effort involved adding depth there while judiciously erasing some of the shading from the left-hand side (directly in front of the light). While I could have gone even further down this road I think that the ball has enough body to make the picture work and I especially like how the edges are very undefined - just the effect I was going for!