One time I had a student who had severe mental issues. He was a fully functional human being, he just had these crazy moods swings. On the lesson sign-up sheet under the "special needs/requests" field, the mother wrote "consider him special". The boy was 11 years old and weighed around 90 pounds. We're about halfway through the lesson, and the kid is in timeout because he was throwing a fit. I hear a child scream from behind me, and as I turned to look, this bastard is chasing another student with a stick he found in the woods. I ran over and took the stick and threw it into the woods. I put him back in timeout and told the floating instructor out there to keep a close eye on him. Not five minutes later, I looked over again to the kid beating my other instructor friend with his ski. I ran over to intervene but the kid came after me. I ended up getting hit in the face with the ski, getting a cut across my cheek, and getting kicked in the shin with ski boots - HARD. I try to restrain the kid but he escaped. Next thing I saw was the kid's dad sprinting over (probably the fastest I've ever seen someone run in ski boots), then absolutely pummeling his kid. Tackled him straight to the ground. Later that day, the dad came back and gave a $300 tip to any instructors involved, $150 of which I received.