user: Question: Who is the opponent when the attendance is 57,331?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'September 9, 1990', 'at Los Angeles Raiders', 'L 14–9', '54,206']
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Attendance" = '57,331';