Hey. How you doing. Congrats for this Funda ball!
Actually here in Mallorca we are playing Fona ball (similiar name) fona means sling. Its similar to yours in some aspects.
Now we are testing it and change some rules every day we play to improve it.
Consists in 3 vs 3. Or 2vs 2.Depends how many we are that day. We wear Jockey Helmets and wood shields. Each one has 5 balls in every quarter. The entire game consists in 4 quarters. There is just one target behind the “enemy”. Hit the target give to you 2 points. Hit a slinger give 1 point and take him out from that quarter. Can’t take the balls from the ground. There are more rules but these are the basics. Because of the helmets we’re close form each other. When they hot you (with tennis balls of course) it burns a little bit.

When we are happy with the rules we gonna write it and I’ll post here if you want.
Thx every body.
(Excuse my English).