Table schema:
CREATE TABLE table_name_41 (previous_team VARCHAR, pos VARCHAR, nationality VARCHAR, nba_years_ VARCHAR, a_ VARCHAR)

Question: What is the previous team of the United States player who had 2 NBA years and played the F position?
SQL: SELECT previous_team FROM table_name_41 WHERE nationality = "united states" AND nba_years_[a_] = 2 AND pos = "f"