I've lost count of how many crossword grids I've cracked using the same few short words for 'ball of yarn'. If the puzzle wants a compact fill, the go-to is 'skein' (5 letters) — it's classic, specific to yarn, and appears in both straightforward and slightly fancier clues. Another neat option is 'hank' (4 letters); it's used when the yarn is looped or tied rather than wound into a perfect sphere. For very short slots, 'wad' (3 letters) can sometimes be clued as a small bundle or lump, though it's less textile-specific.
Beyond those, think of 'ball' itself (4 letters) or 'roll' (4) — simple, literal, and common in casual clues. If the clue leans shop-terminology, 'cone' (4) might fit since some yarns come wound on cones. For messy tangles, solvers sometimes see 'nest' (4) used playfully to describe a tangled skoosh of yarn. In cryptic-style puzzles, 'coil' (4) or even 'wad' can be used more abstractly.
When you're stuck, match the crossing letters and tone: a fancier grid likes 'skein' or 'hank'; a quick, down-to-earth clue will accept 'ball' or 'roll'; and themed or craft-adjacent puzzles might prefer 'cone' or 'nest'. Personally, I get a little giddy when a neat little 'skein' slides into place — it's oddly satisfying.