If you're going to be using sunlight outdoors.. and you're going to be using microphones intended for outdoor use.. then it's an outdoor scene.
A screenplay is a blueprint for making a movie.
I would not use indoor lights or indoor audio equipment for a stadium.
To me...
INT STADIUM would be where you go to buy concessions. You're surrounded by walls and artificial lighting.
EXT STADIUM SEATING In the seats watching the game
EXT STADIUM PARKING LOT Pulling up outdoors
Just be specific and you can avoid confusion.