Muldoon was accomplished at other sports, including lacrosse. He played professionally for a Vancouver club in 1911. He was also an ice dancer who was able to skate, as well as play hockey, while on stilts. In 1914, he took over as the coach and manager of the Portland Rosebuds. For the 1915 season, he changed teams, and went to Seattle to manage a new team in the PCHA, the Metropolitans. He spent eight seasons coaching in Seattle, and amassed a record of 115 wins, 105 losses, and four ties. The Metropolitans competed several times for the Stanley Cup. The Mets played for the Stanley Cup three times under his leadership, and winning it once in 1917 during their first trip. Muldoon was the first and, at age 30, youngest coach of a Stanley Cup Championship team based in the United States.