How many players whose teams were ranked 6 in 1937?
ranked 6 refers to rank = 6; in 1937 refers to year = 1937
SELECT COUNT(DISTINCT T1.playerID) FROM players AS T1 INNER JOIN players_teams AS T2 ON T1.playerID = T2.playerID INNER JOIN teams AS T3 ON T3.tmID = T2.tmID WHERE T3.year = 1937 AND T3.rank = 6