In a little while he returned, carrying a gnarl of pine wood, which he set to blazing at the fire.
The ball is a knob or gnarl from the trunk of a tree, carefully formed into a globular shape.
"contort, twist," 1814, a back-formation from gnarled. As a noun from 1824. Earlier the verb was used in a sense of "to snarl" (1590s).