I think there is a different scenario on Einstein than at a regional field. Einstein reminds me of Disney or the Macy's parade where people get into place hours early to watch an event, but stay for the event. Whereas at a regional, there is more coming and going.
The volunteer
crowd control job description includes:
Prohibit teams from "saving" blocks of seats
Now this is hard! But there is someone to complain to if a team isn't letting you sit. Then the crowd control person can support you in your being allowed to sit. (I've done crowd control. People are "creative" in what they say.)
At the NYC regional, I volunteer as crowd control or safety glasses and go sit with the team I mentor for our matches. Which means I show up right before or a match before ours and then leave the seat. I'm not in the seat all day. And I frequently sit in a seat near our team's seats that has other team's "stuff" marking it. Sometimes this goes ok. Sometimes the team informs me it is there seat. I usually say I'll be gone before their teammate comes back and it is fine. One time, a lady wouldn't let me sit. She had tons of bags on the seat so I picked up the bags and sat down. Turns out she had her leg up on the seat and I sat on her foot. Eek.