TT #206 · Parashas Shoftim · Fifth Aliyah · Passuk 19:05
And one who comes with his fellow into the forest to chop wood, and his hand swings with the axe to cut the tree, and the iron slips from the wood and finds his fellow and he dies – he shall flee to one of these cities and live.
Torah Temimah points to Sifrei Devarim 183.
TT lemma: וּמָצָא אֶת רֵעֵהוּ וָמֵת.
English: ‘And finds his fellow and he dies’ – that the death is immediate.
Derash on immediate causation (Sifrei) — the verse describes a direct, immediate result.
The death must follow directly from the accidental blow for the case to fall under this paradigm.