Ds1 had a child pin him to a wall by his throat within the first term at secondary. My son came from a primary school outside the area so knew no-one, is mild mannered and quiet. This happened in a corridor whilst lining up for a lesson and was completely unprovoked.
What the idiot bully didn't know is that my son does karate and was a high grade. He broke the choke hold and pushed the boy away, the boy tried to kick my son, and my son just kept pushing his leg down so it never made contact with his body. After the third kick my son caught his leg and held it. At that point a teacher came round the corner.
Because they were all year 7's the teacher handed the incident dealing over to the form tutor who saw them daily and also taught them for 1 subject.
Bully child was put in isolation, my son walked free. The choke hold breaking is followed by 1 of 2 actions, either you push them away, or you pull their head down and smash your knee into their face. My son showed he had defended himself, not had a fight. The witnessed attested to that.
I am not a teacher, just a parent. I do know that bully child was pissed off my son wasn't in detention and even asked him why. My son replied, I didn't start a fight.