user: Question: What is the average year that the club located in Enfield was founded with an Unknown coach?
Columns: ['Team', 'Coach', 'Home Ground', 'Location', 'Founded']
Types: ['text', 'text', 'text', 'text', 'real']
Sample row: ['Adelaide Cobras', 'Kris Trajanovski', 'Weigall Oval', 'Plympton', 1972.0]
SQL:

assistant: SELECT AVG("Founded") FROM "Table" WHERE "Coach" = 'Unknown' AND "Location" = 'Enfield';