"What the heck is a sling staff?"
Interesting question, (where do people come up with these things)?
A Sling Staff is a weapon that has been used since at least classical Roman times as a military projectile weapon.
It consists of a staff, from four to six feet long, that has a post set in the top, One end of a sling is anchored the base of the post the other end of the sling is formed into a loop, or is attached to a metal ring (which works better).
To use a sling staff, you slip the ring over the post and load the sling pouch with a bullet or stone.
The staff is then swung over head two handed, flinging the bullet forward with considerable force. The sling and the staff part of the device act as levers to produce much more force and velocity that could be achieved with the arm alone and the weapon is quite capable of killing a human being. The weapon was used into the Middle Ages.
So there you have it, the sling staff.