user: Question: What opponents played Waldstadion in a game?
Columns: ['Week', 'Date', 'Kickoff', 'Opponent', 'Final score', 'Team record', 'Game site', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text', 'real']
Sample row: [1.0, 'Saturday, April 3', '7:00 p.m.', 'at Frankfurt Galaxy', 'L 11–34', '0–1', 'Waldstadion', 21269.0]
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Game site" = 'Waldstadion';