Hey Michael, this can be achieved using conditional visibility.. The way that the conditional visibility fields work is as OR statements. So you could show a specific field if someone selects event x, or event y -- and it wouldn't be shown if they select event z. You would probably want to use "show" instead of "hide" as I have in my example below -- unless you want something to be based on an AND statement. If you want a field to show if multiple criteria are met, then take a
look at this thread. 
Hope this helps, but let me know if I can explain this any further using your specific situation!