The school was following the law. They were compelled to allow the boy to play. I don't think you can successfully sue someone for obeying the law.
I believe anyone can sue anyone or thing. If there is a possibility ,even remote, of relief the case can be accepted.
In this case,I would guess, that the law allowing a man to play on women’s teams was not followed explicitly. There could be culpability.
What needs to be done is the children/family members of charlie baker and others who approved this law need to be violently attacked in a similar manner. File it under restorative justice