user: Question: Who was the opponent when there was 81 rushing yards?
Columns: ['Rank', 'Player', 'Year', 'Opponent', 'Passing yards', 'Rushing yards', 'Total offense']
Types: ['real', 'text', 'real', 'text', 'real', 'real', 'real']
Sample row: [1.0, 'Devin Gardner', 2013.0, 'Indiana', 503.0, 81.0, 584.0]
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Rushing yards" = 81.0;