user: Question: What category is Matthew Barton?
Columns: ['Outcome', 'Date', 'Category', 'Surface', 'Opponent', 'Score']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Winner', '11 May 2009', 'Challenger', 'Clay', 'Carsten Ball', '6–7 (4–7) , 6–4, 6–3']
SQL:

assistant: SELECT "Category" FROM "Table" WHERE "Opponent" = 'Matthew Barton';