N.G.
The ridiculous thing about schools is that the person who fights back always gets the same punishment that the 'bully' gets, which is ridiculous. I know that this is largely due to the fact that there simply aren't enough school officials to take the time to determine and issue good and proper discipline, and to discourage fighting completely, but imagine if our legal system punished victims the same way we punished perpetrators. Ridiculous!
So, to answer your question, I would never punish my child for defending herself, and I would hold any school accountable who did punish her for defending herself. I would punish her greatly for starting a fight, and would support any school who punished her for the same.