Was it one single impact at a certain place at a certain time?
Or a decade and a half of repeated blows?
Perhaps it was just a weak vein that had been there all along. Perhaps that single perfectly executed left hook from his southpaw opponent was enough to trigger that ticking time bomb. Or perhaps that left hook was just too perfect. Perhaps it would have felled any opponent.
In the long run, it doesn’t matter. He lay there for the ten count and he continued to lie there as his trainer tried to revive him.