https://youtu.be/uFZJM0gb0ZA?t=80

Apparently stone wars between neighborhoods were regular practice in the early 1900's in Athens resulting to injuries and deaths, but this video is from a movie so if you watch it in slo-mo you'll see that some act like they are throwing/slinging but they aren't.
the slings seem to be split pouches.

I looked into it after a comment from jackinati on my video about  tsubute, Inji-uchi, Seokjeon.