user: Question: When the Away team scored 12.9 (81), what was the average Crowd size?
Columns: ['Home team', 'Home team score', 'Away team', 'Away team score', 'Venue', 'Crowd', 'Date']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'text']
Sample row: ['North Melbourne', '15.7 (97)', 'St Kilda', '15.18 (108)', 'Arden Street Oval', 8000.0, '29 August 1936']
SQL:

assistant: SELECT AVG("Crowd") FROM "Table" WHERE "Away team score" = '12.9 (81)';