Table: east_germany_footballers
Columns: position
appearances
goals
first_appearance
last_appearance

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 east_germany_footballers WHERE "last_appearance" < 1984 AND "appearances" > 17 AND "first_appearance" < 1961 AND "position" = 'mf'