Have the other parents been told about your ds's problems? Would it help if you tried to build bridges? Would it be helpful if you went in and spoke to the class? Or tried to make friends with the parents and explain?
Because if they are not given any information, if all they hear is that their children are being hurt, then you can understand that they are getting upset.
If it was my child being hurt (well, actually it was a few years ago, and he was getting too scared to go to school), then there are a few things I would like to reassure me:
an explanation of why this keeps reoccurring yet the usual punishments are not being meted out (if I was told that there was suspected SN that would make things easier to understand)
a plan for how the school are going to deal with it in such a way as meets the needs of your child, yet keeps my child safe (e.g. extra playground supervision, instructions given to the other children on how not to wind him up)
a plan for what you want the other children to be told (children need to know why X is punished for pushing, but not Y)
the reassurance that you recognise my fears and those of my dc
In return you would have my sympathy and I would do everything I could to train my own dc to behave in a way that made things easier for yours. And maybe we could all gang up on the school if they were not providing adequate supervision.
But as a parent I remember how difficult it is to try to deal with a child who doesn't want to go to school because he keeps getting knocked down and doesn't feel safe. I wouldn't go to work under those conditions, however sorry I might feel for a fellow colleague with SN.
The answer must lie with the school. But in the meantime I would try my hardest to make the other parents my allies.