Commentary for Bava Kamma 34:4

It seems that if a person throws a rock or arrow towards a vessel and another person comes along and shatters the vessel before the projectile strikes it, certainly the one who shattered the vessel (and not the one who threw the rock) is liable. In this instance we do not apply the rationale of “the second one broke the vessel.” simple logic call for us to distinguish between throwing a rock (toward a vessel) and throwing the vessel itself.