What would happen?????

I think what you are asking is if you get hit hard in the spine will it stunt yor growth. Correct? Answer simply is: not likely, but could happen in rare cases. If you severe the cord or severely damage a nerve root, sure, you could become a parapalegic and not "grow" in your lower half. Growth plates are found in every bone in your body, and getting hit hard in the bone won't necessarily hurt your growth plate, but may damage the bone. The long and short is, I don't think you have too much to worry about.