In West Philly, we called it “caps”. Sometimes “Skelly” which I always thought was short for skeleton. We packed our decorked bottle caps with dirt. We took turns looking out for cars. I am teaching it at recess at our K-8 school for TV Turn-off Week. My husband is donating his plastic Odwalla (SF Bay Area exclusive) and metal Stewarts root beer caps to the cause. Your rules are really helpful for refreshing my memory about the skull section conseqences. I intend to give the kids several sets of your rules and let them go for it. I hope with practice that they are able to improve upon our old techniques. A fellow parent from NJ hipped me to your fab site. Eyewater is rolling mourning childhood’s end :{