When you go to a baseball game...(read below)?

Depends on the stadium. Usually the really good seats are checked at the top of the aisle. But to buy a nosebleed and move down is pretty common. Sit in the seat you bought and look for some empty seats - while the game is being played- and just act like you belong. It's worth a try. I do it all the time. Problem is, you miss some of the game, walking around.