Fastballs rhymes with:
basketball's, basketballs, football's, footballs, meatballs, softballs, spitball's, basketball's, basketballs, butterballs, eyeballs, fireballs, football's, footballs, handballs, meatballs, mothballs, oddballs, snowball's, snowballs, softballs, spaceballs, spitball's, trackballs