@rdm@futzle I guess springy wires pop apart to let the tennis balls in when pushed down on/rolled over the balls, but the weight of the balls inside isn't enough to pop them apart and escape
@rdm@futzle I wish the tennis court over the road from me had one, I'd stand and watch it! Instead they seem to just rely on volunteering the youngest person to run around and pick them up ... or did, I suspect the courts and small clubhouse is now awaiting the bulldozer & redevelopment as a block of townhouses