user: Question: What was the opponent for July 21?
Columns: ['Date', 'Opponent', 'Score', 'Loss', 'Attendance', 'Record']
Types: ['text', 'text', 'text', 'text', 'real', 'text']
Sample row: ['July 1', '@ Cardinals', '6–0', 'Kennedy (4–8)', 40128.0, '27–51']
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Date" = 'July 21';