CREATE TABLE table_name_57 (round NUMBER, position VARCHAR2, player VARCHAR2)

Name the Round which has a Position of defensive back and corey chavous?
SELECT MIN(round) FROM table_name_57 WHERE position = "defensive back" AND player = "corey chavous"
SELECT MIN("round") FROM "table_name_57" WHERE "corey chavous" = "player" AND "defensive back" = "position"