And here in San Antonio we have an extremely diverse set of schools. You sign up to teach in a district. You do not sign up for a school. You have no idea what you are going to teach or if you will be in a school that is monitored by on site policemen and police dogs that check lockers weekly. Just being a teacher in some areas in and of itself is dangerous.
So you may not have signed a contract that doesn't put person or property in jeopardy but it does happen. And it happens when you aren't even in the military.