John Gill Commentary Numbers 35:22

"But if he thrust him suddenly without enmity, or hurled upon him anything without lying in wait," — Numbers 35:22 (ASV)

But if he thrust him suddenly, without enmity
Push him from a precipice, before he is aware, without any malicious design against his life, but merely through accident:

or have cast upon him anything ;
from the top of a house, or from a building he is pulling down, or pushes a bowing wall upon him, not knowing that he is passing by it:

and without lying of wait :
or having contrived to do it, just as he goes along, or in any other similar way.