That called an oblique kick. While not exactly illegal in mma, it's a huge dick move imo. Only use it if you don't mind ending someone's career. Make sure you shadow box in your steel toes every now and then. It feels much different than being barefooted and you run the risk of losing your footing in a fight if you're not used to the extra weight added to your foot work Savate is a pretty cool martial art. Europeans had mma style sword fighting. I wish we passed it down as culture the way the Japanese and other asian countries do.