user: Question: What Nationality has the Player of Marcus Walker?
Columns: ['Season', 'Player', 'Position', 'Nationality', 'Team']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['2003-04', 'Darrell Lewis', 'Guard', 'USA / Iceland', 'Grindavík']
SQL:

assistant: SELECT "Nationality" FROM "Table" WHERE "Player" = 'Marcus Walker';