Database: video_game
Question: Return the average number of units sold in millions among games played by players who have the position Guard.
SQL:
SELECT avg(Units_sold_Millions) FROM game AS T1 JOIN game_player AS T2 ON T1.Game_ID  =  T2.Game_ID JOIN player AS T3 ON T2.Player_ID  =  T3.Player_ID WHERE T3.Position  =  "Guard"