Or, really, any sporting event.
The colleges in my state have all sent out the list of media policies for spring football practice. Almost all of them put restrictions on what can and can't be filmed or photographed, what periods reporters can observe, cell phone usage at practice, etc. I might go cover a minor league baseball game tonight. It's pretty loose as far as access, but I'm still not allowed in the dugout even if it's the quickest route from one camera vantage point to another. As someone else said, see what the Secret Service does to you if you try to wander around at a presidential appearance. It'll make that Augusta security guard look like Officer Friendly.
Credentials come with access, but also restrictions to help the actual event go on as expected. Every credential. Every venue.