Or maybe getting hit in the head by a rock launched from a sling is enough to make a personโs head basically explode.
Seriously, a competent sling user can easily kill someone with one.
I found a quick little video demonstration of a guy using a sling and stone against a ballistic gel head.
Just judging off of that, I would agree that weird tumors would not need to be involved for a sling to kill a large fellow.