Hum, I've tried karate for a while. But eventually I just accepted that I hate sports and the bigger kids would still take my lunch money no matter what.
But seriously now, that's a really interesting concept. And I agree with you, for it to work it should be VERY clean, otherwise it will look confusing. I like that you used grayscale, no land texture or gradients and kept it clean, its a real all round concept and you should definitively use it again!