Ouch !
Now I fully understand. So the balls might be double effective: Once when they hit and again when they are lying on the floor ... at least when there are more than one on the ground.
In school we used to have this in a moderated version: Wettened paper balls blown through a blowpipe, e.g. a ballpoint pen sleeve. Quite disgusting ...
The more sophisticated version we did in the 70s in our outdoor games was shooting (window)putty bullets trough about 1m long solid plastic pipes (normally used for electric installations). When you were hit by these on your bare skin (short trousers etc) you could really well feel it ;-) .
Well, nowadays the youngsters play paintball
Thanks for the explanations
regards
Andreas