I spar all of my instructors just about every class; our school is very fighting intensive and emphasizes learning how to adapt to any fighting situation via experience rather than repeated drills. We always get banged up, bruised, jammed fingers and toes, but we rarely have any serious injuries. My most serious injury came during my black belt review, where I was faked out by my sensei with a low roundhouse which turned into a heel kick. I caught the foot below the temple and don't remember a whole lot. Granted, it was partially my fault - I dropped my guard and moved in for a counter, and it was about an hour into the full-contact fighting segment of the review after all the other requirements. It suffices to say that both parties involved felt bad