פּירוש אויף במדבר 35:23

או בכל אבן אשר ימות בה OR WITH ANY STONE WHEREBY ONE MAY DIE, he smote him.

ויפל עליו, “he caused it to fall upon him.” This verse caused our sages (Makkot 7) to determine that if someone kills unintentionally by dropping something while lowering it he must go to the city of refuge, but if it occurred while lifting the object he does not go.

ויפל עליו “and he threw it down upon him;” from the wording of this verse the Rabbis concluded that killing by dropping something on the victim makes the killer subject to spending the rest of his life until the death of the High Priest in a city of refuge. If the killer had looked at what was below him he would have seen that dropping an object or throwing an object down was something dangerous. (Talmud tractate Makkot folio 7) On the other hand, if the victim was struck by the killer having thrown something up into the air, this is considered an accident, and the person who had thrown the object does not have to be confined to the city of refuge. The basic principle is that one has to look in front if there are obstacles, but not behind or above. Normal people do not look in all directions before throwing an object.

בלא ראות — i.e. that he (the slayer) did not see him (Not: without anyone having seen him, i.e. that there were no witnesses).

ויפל עליו AND HE CAST IT UPON HIM — From here (i.e. from these words) they (the Rabbis) said: he who kills inadvertently by way of a falling movement goes into exile (i.e. must escape to and reside in a city of refuge); he who kills by way of an upward movement does not go into exile (Makkot 7b; cf. our Note on Exodus 21:13).