What about the child who is happily violent though?

I'm not really having a go (I've got my tongue firmly in my cheek). However, not all violent behaviour stems from a child being unhappy at school.I've had to deal with more than one incident of a teenager being extremely violent, or threatening extreme violence, and that originated outside school and was brought in. We are not always to blame for everything. I can assure you that it is terrifying to be faced by a very large teenage boy armed with a knife, who wants to "cut up" three boys because his family has fallen out with theirs.

I am not sure that there is a safe way to "restrain" someone like that - no matter what it is proposed young teachers should learn. Would anyone else attempt to restrain a violent teenager out in the street? What consequences could there be? What is minimum force? Any decision to restrain a violent child or remove them from a dangerous or disruptive situation is fraught with worry and complications. I know because I've been there.It is not a decision to be taken lightly, no matter how well trained you are.