That's actually what they were originally used for. Sailors, in the day of wind propelled sailing ships, would use them to throw over lead lines. They would tie the lead line in a monkeyfists knot over ballast or lead shot and sling it to shore or a waiting boat. The sailors on the receiving end would use the lead line to pull over the heavier rope. Quiet literally "slung shot".

The sailors would also attach short loops to the knotted weight and use them in brawls. This subsequently lead to their outlaw.