 Complete the following phrase:  Nadin began refereeing ice hockey at the University of Toronto, when he was 17 years old. He was encouraged to officiate by teammates in the interfaculty league, and he said that he enjoyed refereeing more than playing. He later became referee-in-chief of the school league, officiated in the church leagues of Toronto, and moved onto the Ontario Hockey Association OHA. Nadin later refereed games at the Memorial Cup, Allan Cup, Centennial Cup, approximately 100 international games, and was offered a place in the National Hockey League, but ended up refereeing in the Eastern Hockey League. He twice refereed matches between the Canada mens national ice hockey team and the Soviet Union national ice hockey team at Maple Leaf Gardens, first on January 10, 1967, then on January 19, 1969. Nadin made his debut at an International Ice Hockey Federation IIHF event, refereeing seven games at the 1972 Winter Olympics in Sapporo. Later in the same year, he conducted refereeing clinics for Russian ice officials, shortly before the Summit Series took place. Nadin returned to the international stage, refereeing games at the 