The answer is yes. In most mixed martial arts leagues you are required to be barefoot. Sometimes they allow a compression sleeve around your foot to get better grip. Here is a video compilation of head kick knockouts!
We all know there are so many laws that you are probably breaking 5 of them a day without even knowing about it. So is driving barefoot illegal? The answer is yes in a lot of states. We live in a world where there are rules just to have rules. A lot of them don't make any sense. Often times in these states you can drive in high heels but you can't drive barefooted. Also a lot of times stores don't want you coming in with no shoes on. Why? Do they think their floor will get to many skin cells on it or is it some kind of OSHA law / rule? Here is one man admittedly breaking the law in New Jersey. He is ripping the system and driving chimp feet style.