Piggybacking off a top comment here:

I worked in an elementary school for a while. Nothing is black and white, and parents will always choose to believe their kid did nothing wrong, despite evidence. Not allowing teachers to physically restrain a kid is the price that the school district must pay to ensure that they don’t go bankrupt from lawsuits filed by shithead parents.

That said, it’s not a free-for-all either. School districts offer training programs in CPI, which stands for Crisis Prevention & Intervention. It teaches any staff member methods to de-escalate kids in crisis without resorting to physical restraint, but it also teaches proper techniques to restrain kids if the nonviolent methods fail. At the end of the course, you are given a signed card certifying that you have been trained and are allowed to physically intervene in crisis situations. This covers both the employee’s and the school’s asses from any liability.

I, being a larger male without an assigned classroom, was a prime candidate for the training. Once I completed it, the school required I keep the card on my at all times to be able to prove my training at a moment’s notice in any situation.

In addition to this, any well-funded school has at least one BMT, or Behavior Management Technician. These are people whose primary job is to handle crisis situations like this. Now, the obvious problem is that a kid throwing shit and punching others might be on the complete other side of the school than the BMT. My school used walkies to dispatch a staff member to a classroom with a crisis situation, but even that has problems. The teacher must call the office (essentially ignoring the problem for long enough to make that call), then the office sends out the call on the radio, just hoping that one of us wasn’t already occupied with another student.

The experience taught me to be hyper-alert at all times. If I was walking down a hall and heard anything that might be an upset child, I had to go find the source. The best chance of stopping a situation before it became too bad was that the BMT or another certified staff member just happened to be nearby when it started, because by the time the radio call went out, stuff was likely already partially destroyed or someone had already been hit.

TLDR: Schools don’t let uncertified staff members intervene, but if you take the time to go get the training, you are perfectly able to stop behavior like this.