Table schema:
CREATE TABLE table_name_52 (goals INTEGER, position VARCHAR, first_appearance VARCHAR, last_appearance VARCHAR, appearances VARCHAR)

Question: What is the average goals when the last appearance was before 1984, there were more than 17 appearances, the first appearance was before 1961 and the position was mf?
SQL: SELECT AVG(goals) FROM table_name_52 WHERE last_appearance < 1984 AND appearances > 17 AND first_appearance < 1961 AND position = "mf"