It's difficult to explain ASD to those that don't have it.
I didn't respond with violence as a child, but I can see why some do.
Imagine a world where the "volume" is set to maximum, for everything.
A whiff of perfume or aftershave is like being in a smoke-filled building.
Clothes feel like sandpaper.
Small noises can't be filtered out. Loud noises are terrifyingly loud.
Lighting is perhaps impossibly bright/flickers in a way that cuts across all concentration.
People wave their arms about and their faces contort into all sorts of shapes for reasons they never say. Then when we don't understand or didn't switch attention to them fast enough, they often shout, which makes it even worse. It takes a long time to decode it all.
Being touched is often so 'painful'/scary, even fairly light touches.
Unexpected events or unexpected changes in our world are a total shock. We just can't work out what happened.
Imagine coping with that every day, all day.
Some kid knocks into you, and it becomes "the final straw". The lad just can't handle it any more. I used to shut down - just go completely blank. It was my way of coping. It still is. Others respond as they would have done as toddlers - wild behaviour that needs help with controlling it, and help controlling the 'volume' on the world around them.
It takes a whole-school approach to really make it work. A quiet zone or room where we can just unwind, away from people for a while, until the noise/sensations die down to a dull roar instead of a hurricane. A sense of routine. Classmates who are aware of the sensitivites and don't use them as a way to bully the others.
Your local autism charity can be a source of good support, too.