Catapult balls that are constructed of broken stone and low-grade masonry will shatter when hitting a hard object. Ballista bolts surprisingly heavy and will split into dangerous splinters when they hit a surface. Either has the potential for breaking apart and causing damage with shrapnel:
All creatures within the orange hexes above can potentially take damage. Each are "attacked" by a d20; those that are hit will suffer shrapnel damage from the weapon that has been used.