My son keeps getting hurt at school

My 6 year old little boy has ASD and struggles to communicate. My son is in a main stream school but spends most of his day in a part of the school with other children like him. He’s is not aggressive and is a sweet gentle little boy but he always seem to get hurt by other children when they lash out. Today I had to go collect him from school because another child flung a toy and it hit him in the head, he has a massive lump and a bruise on the side of his head and I had to go get him checked. 

what do I do in this situation.