CREATE TABLE table_204_70 (id NUMBER, "pick #" NUMBER, "nfl team" CLOB, "player" CLOB, "position" CLOB, "college" CLOB)

what is the average number of defensive backs chosen in the seventh round ?
SELECT COUNT(*) FROM table_204_70 WHERE "position" = 'defensive back'
SELECT COUNT(*) FROM "table_204_70" WHERE "position" = 'defensive back'