user: Question: What is the average crowd size at Princes Park?
Columns: ['Home team', 'Home team score', 'Away team', 'Away team score', 'Venue', 'Crowd', 'Date']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'text']
Sample row: ['Footscray', '9.11 (65)', 'Hawthorn', '14.19 (103)', 'Western Oval', 12839.0, '1 September 1979']
SQL:

assistant: SELECT AVG("Crowd") FROM "Table" WHERE "Venue" = 'Princes Park';