CREATE TABLE table_name_81 (year NUMBER, points VARCHAR2, class VARCHAR2, team VARCHAR2)

In what Year did the Norton Team have 0 Points and 350cc Class?
SELECT AVG(year) FROM table_name_81 WHERE class = "350cc" AND team = "norton" AND points < 0
SELECT AVG("year") FROM "table_name_81" WHERE "350cc" = "class" AND "norton" = "team" AND "points" < 0