In Kyokusin Karate, we trained in kumite (sparring) at least once week fighting every person in the dojo, full contact, bare knuckle and feet, with absolutely no holds bared and no one to check to see if anyone forgot to remove a ruby ring or two. The only protection we had was blocking, hitting harder to discourage our opponents, and a athletic cup (more or less for show, as it didn't seem to do much). One of my friends, Steve, ran into a ruby ring and wore an impression of the carat weight stone for the next several weeks (above his right eyebrow).
The most important things I learned in these classes was to block very hard and use my blocks as strikes to get the attacker's attention. This would become very important to me later in life. We also learned to break rocks which became valuable in high school. One day, I was showing off to some students during PE by breaking a rock. The news spread like wildfire, and soon few would dare to cross my path. But a rock is a rock and not a person and breaking a rock means little. But back in the 60s it was almost unheard of. I suspect each time the event was told over and over it was likely embellished until the stone grew into a boulder.