user: Question: What was the manner of departure for the vacancy date of 20 September 2009?
Columns: ['Team', 'Outgoing manager', 'Manner of departure', 'Date of vacancy', 'Replaced by', 'Date of appointment', 'Position in table']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Arminia Bielefeld', 'Jörg Berger', 'Mutual consent', '30 June 2009', 'Thomas Gerstner', '1 July 2009', 'Pre-season']
SQL:

assistant: SELECT "Manner of departure" FROM "Table" WHERE "Date of vacancy" = '20 September 2009';