A few things:
- There will be about 1/3 of the flight area behind the stadium from your perspective where you will not be able to see if there are people you are flying over. Suggest an observer on the opposite side with a radio to help you. This is not an FAR p. 107.33 Visual Observer; you are keeping your drone at an altitude where you have direct sight of it at all times and are directly watching it with your own eyes. This is just someone helping you be safe and comply with the OOP rules by telling you about people on the ground you can't see.
- Take 30 minutes to write up a simple detailed description of the mission you plan, with diagrams showing where your planning to take off and land, flight path, any additional helper's location(s), the plan for attendee safety, what you plan to record and how you plan to use it, etc.
- See if you can meet with the facility manager and event organizers ahead of time to get their buy-in. If the captured media isn't of commercial value, offer to share the footage / stills with them. if they give permission, ask to speak to security to loop them in before the event, and check in before you fly during the event.
If pertinent authorities refuse, I recommend you just abandon the project and go cry in a few beers. That's the smart move. If there's no TFR and the airspace is otherwise unencumbered, you could go ahead but you'll be asking for trouble and making enemies you don't want to make. Same risk if you go and do it without asking.
Now, if doing this when it's empty and not in use? Forget all those hoops above and just go do it (again, assuming the airspace is unrestricted).