off the puck in the defensive zone, but to disallow checking of players not in possession of the puck. In October 1936, Duncan tested a change to avoid automatic offside infractions in a match between the hometown Ottawa Senators and the visiting Springfield Indians. In a January 1937 game, he experimented with a single blue-line at centre ice as per a suggestion by Frank Boucher to cut down on the number of offside infractions in a game. Rules of play at the time stated that a puck could not be passed over a blue line by either team. In February 1937, the LIHG adopted the playing rules of the CAHA for international matches with a few minor exceptions. Duncan felt the differences were insignificant and the decision promoted global uniformity in playing the game. In April 1937, he appointed NHL referee Clarence Campbell as the interpreter of the playing rules and a reference person for branches in the CAHA. Duncan recycled an idea from Frank Patrick and experimented with five-man hockey in the Ottawa and District Senior Hockey League during the 1939–40 regular season, then six men for the playoffs. The innovation was intended to produce more individual play, stick handling and skilled players. Journalist Scott Young criticized the experiment; he felt that stick handling was less important with the increase of the number of substitutes available during a game and that the change would actually promote use of more substitutes as players tired. In May 1941, Duncan was critical of the lack of consistency in refereeing across Canada. He felt that referees in Eastern Canada were more strict in the interest of safety, whereas the Western Canada played a rougher more dangerous style. Duncan and NHL rules committee chairman Frank Boucher introduced the centre red line to the ice hockey rink in the 1943–44 season, in an effort to open up the game by reducing the number of offside infractions and create excitement with quicker counter-attacks. The change allowed the defending team to pass the puck to out of their own zone up to the red line, instead of being required to skate over the nearest blue line then pass the puck forward. In 1947, Duncan sought for the CAHA to implement European rules of play that restricted checking to a team's defensive zone, since he wanted to see a wide-open style of play that made it easier to