I would like to no the laws on what would happen if a parent or stepparent was to hit there 16 year old boy in self defense if that child was to come at him or her first.

What is the home situation like?

If it is self defense, then it is, and that would be your defense if the state presses charges.
Parents should have called the police as soon as it happened to report the assault that the child just did.

Hitting someone, assault, if they are a child, child abuse also.