CREATE TABLE table_28311 ("Rank" FLOAT, "Player" TEXT, "Year" FLOAT, "Opponent" TEXT, "Passing yards" FLOAT, "Rushing yards" FLOAT, "Total offense" FLOAT)

Who was the opponent when there was 81 rushing yards?
SELECT "Opponent" FROM table_28311 WHERE "Rushing yards" = '81'
SELECT "Opponent" FROM "table_28311" WHERE "Rushing yards" = '81'