I have heard of stories of students getting a little wild with the master during sparring. And they end up getting blasted across the room.
One particular one that stands out is a grappling class where a student was in a hold and tapping out but the the other student did not let go until he started screaming. That student was out of action for a couple of weeks. No major damage, but he was limping for awhile. The teacher ripped that student a new one for not being more aware. The teacher also told the class to be careful at all times.
Even when everything got back normal, he was not the most popular guy to grapple with.
The student ended up weeding himself out and left.