Launching a DSMB

[stretchthepenn]

How would a rinky ding 4" double ender that would slide freely on a string under tension, a foot away from the diver face, whack the diver in the face & injure the diver?.

Easily. Maybe the double-ender snags on a knot in the string and whips around. Maybe the line pops out of the diver's guide-hand and goes toward the diver's face. Maybe the string gets caught in a worn gate or a rough spot and pops the gate.

Do what you want, mang, but I ain't running a fast-moving string through a free-floating chunk of metal, and I don't suggest anyone else does it either.