user: Question: On what Surface was the match with a Score of 6–4, 6–3 and Runner-up Outcome played?
Columns: ['Outcome', 'Date', 'Tournament', 'Surface', 'Partner', 'Opponents', 'Score']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Runner-up', 'August 4, 2003', 'Spain F15, Denia', 'Clay', 'Karim Maamoun', 'Jordi Marse-Vidri & Daniel Muñoz-de la Nava', '6–7 (1–7) , 7–6 (8–6) , 6–4']
SQL:

assistant: SELECT "Surface" FROM "Table" WHERE "Outcome" = 'Runner-up' AND "Score" = '6–4, 6–3';