Knitting - Basic Techniques
You can make a bouncy, ball-like motif by increasing (knitting 3 or 5 stitches in 1 stitch), working several rows on only those stitches, then decreasing back to 1 stitch. If the stitches are worked in reverse stockinette stitch, you get a more 3-dimensional effect.
Bobbles are often worked as part of the stitch pattern for Aran sweaters. Bobbles can also be worked with a crochet hook.