user: Question: Which opponent was played at Forbes Field after week 4?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Game Site']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'Sunday September 20', 'New York Giants', 'L 23–2', 'Forbes Field']
SQL:

assistant: SELECT "Opponent" FROM "Table" WHERE "Game Site" = 'Forbes Field' AND "Week" > 4.0;