Edited, Scudbar I needed to read your post more thoroughly.
OK, got ya,
These restrictions are simply not reasonable.
And I agree.
But the teacher didn't find the shirt disruptive, and the disruption wasn't about the shirt.
The teacher didn't like it or didn't fully understand the School's dress code. He tried to make the kid take it off, the kid refused.
Then the other kids went crazy over it yelling, making noise, being unruly teenagers.
The teacher is claiming the kid got belligerent with him over it and that is what drove the other kids into a frenzy.
The school called in the cops to
quell the riot.
Then, in the School Office, they asked the kid to take off the shirt again, again he refused, they suspended the kid blaming him, not the teacher or the other kids, for the disturbance, and had the cops arrest him for it.
The teacher was wrong to ask the kid to take off the shirt.
The teacher was really wrong to do it in the cafeteria instead of somewhere more controlled.
The principle is wrong for calling the cops, can't handle the kids, shouldn't be doing the job.
The cops were right in responding to the school's request for help, but they were wrong to arrest the kid. They should have known better.
In fact, the Officers should have recognized the real trouble with all this, called a Police Chief in, had a good talk with the principle and released his officers back to their other assignments and duties. Police Chief then should have called the School District's Superintendent and let him/her know that this School Principle is about to get the District and maybe the City sued.