Let the director know that you would like to schedule a conference or meeting and that you would like your daughters teacher present as well. Explain, in full detail like you did here on mamasource, the exact scenario of what took place. Ask questions about the discipline procedures at the school, do the teachers know and understand these procedures and ask why this particular child was not discipline at the time of the incident. If the teacher is aware of behavior problems with this child, why did she not take action against his behavior? They should not excuse his behavior just because "they know how he is". That gives them more reason to take action to say that this behavior is not tolerated.
Don't be discouraged. This is the safety of YOUR child and the safety of the other classmates as well. Ask what will be done in the future so that this incident doesn't happen again, to your daughter or to any other child in this particular class. By doing so, you are making the director aware of what you observed and that action may be taken if another incident arises.
Good Luck.