You seem to be doing a lot of "backseat driving" in order to justify this man's actions, and you also seem to know very little about how the education system works. I'm a college professor, my dad taught high school for forty years and retired as an administrator, my brother and sister-in-law are both teachers, and many people in my family are in the profession. So, let me fill you in on some things about education:
Many--most, actually--schools have a zero tolerance policy on student/teacher assault. In almost all cases, this included teachers who feel that they're "provoked" by the student in question. Many teachers have lost careers and pensions for acting in situations where they felt they had to physically defend themselves. The way this has been handled does not seem typical, based on my knowledge of the education system.
An administrative/desk job is almost always a promotion, not something that they'd give you as a way to keep you out of the classroom and away from kids. It certainly wouldn't be given to someone as "punishment" for assaulting a student.
While free speech isn't always completely protected inside the walls of a high school, a teacher or principal would have to have a justified reason for telling a student not to wear a shirt (e.g., it features profanity or something that goes against the school's student behavioral code). No article has made mention of any such provision.
"You travel alone because other people are only there to remind you how much that hook hurts that we all bit down on. Wait for that one day we can bite free and get back out there in space where we belong, sail back over water, over skies, into space, the hook finally out of our mouths and we wander back out there in space spawning to other planets never to return hurrah to earth and we'll look back and can't even see these lives here anymore. Only the taste of blood to remind us we ever existed. The earth is small. We're gone. We're dead. We're safe."
-John Guare, Landscape of the Body