Table schema:
CREATE TABLE table_name_87 (field_goals INTEGER, touchdowns VARCHAR, player VARCHAR, points VARCHAR, extra_points VARCHAR)

Question: When Herb Graver played, how many field goals were made when there were more than 50 points, less than 15 touchdowns, and more than 0 extra points?
SQL: SELECT AVG(field_goals) FROM table_name_87 WHERE points > 50 AND extra_points > 0 AND player = "herb graver" AND touchdowns < 15