What amount force would be required for massive cranial hemorrhaging to occur?

Depends: Sometimes in the elderly, only a small blow to the head, just a bump really, can set off subdural bleeding, which can grow slowly or quickly. For healthy young adults substantial force is required, blunt object, fall from height. However, the effects of a small amount of bleeding in the brain of young person can worse than in elderly, whose brains have shrunk & don't get the high pressures.