yep, I'm afraid this is getting more and more normal in schools, partially due to lack of specialist placements, partially funding and partially due to lack of parental support.
I work in mainstream but mainly with the more challenging students, I have been kicked, punched, pinched, scratched, slapped, bitten, had my hair pulled and had items thrown at me ranging from a pencil to a table. Not all by the same child and not all by children with SEN. Some of it is children who genuinely can't control it, some of it is out of frustration, some of it is learned behaviour that they are copying from somewhere else, some of it is poor parenting leading to children not knowing boundaries and the one that upsets me most is some of it is due to traumatic backgrounds.
The problem is, 1- without parental support there is little the school can do. For example a child got sent home for violence, parents took them to McDonalds and for a lovely day out in the sunshine, therefore get sent home = get to do nice things. I have regularly seen parents blame the teachers for their child's shitty behaviour so in those kids minds it doesn't matter if the teacher tells the parents, the parents are going to blame the teacher anyway.
2 - there are only so many adjustments a mainstream school can make. Not just because of funding. For example I spend a lot of time in our sensory room with a child who simply can't handle the noise and over stimulation of 30 children in a classroom, child then lashes out, all I can do is move other children away from them and get them somewhere safe, which is usually when I get hurt. Its not their fault, it's not the parents fault. They would be much happier in a smaller, quieter class, with the facilities they need but the LA says we can meet their needs.
3- there are children living in homes where the shouting, violence, throwing things is normalised, so schools are not only teaching them social skills but having to get them to unlearn the example they have been set at home. I'll never forget the child who pulled my face round by my hair to get my attention when I didn't answer quick enough because "That's what Daddy does." Poor child genuinely thought that was normal.
All bad behaviour has a reason, whether it is SEN, attention seeking, poor examples/poor parenting or a reaction to something horrible, we might not be able to see what the reason is, or it might seem a stupid reason to an adult but there will be a reason.