None of the rounds has Roger Williamson as a driver.
CREATE TABLE "championship_drivers_and_constructors" (
  "entrant" text,
  "constructor" text,
  "chassis" text,
  "engine" text,
  "tyre" text,
  "driver" text,
  "rounds" text
);
SELECT "rounds" FROM "championship_drivers_and_constructors" WHERE "driver"='roger williamson';