There are many footballers who have converted from one football code to another at a professional or representative level. In some cases, the player may also return to the original code, so the traffic is not merely one way. In some countries, such as the United Kingdom, United States, Ireland and Australia, where multiple codes are popular, and the practice of switching codes is relatively common, such players are known as code converts or code hoppers. In Australia, star code converts can have a substantial impact on the games. For instance, Dally Messenger's defection from rugby union to rugby league was considered a pivotal moment in the establishment of the latter over other codes in Australia. Globalisation is increasing the opportunities for players to transfer to different countries and to different professional sports, including the forms of football. From American football American football to Association football American football to Australian rules football American football to Canadian football American football and Canadian football are very similar gridiron codes; talented Canadian youth players are often recruited by American universities offering scholarships, and conversely the Canadian Football League enforces roster minimums for Canadian-trained players to prevent its clubs from fielding American-dominated teams. The CFL and NFL competed for the same player pool in their earlier years before the CFL settled into a de facto (and from time to time formal) developmental role to its American counterpart. Dozens of professional players move between these codes' top professional leagues every year, making any attempt at a list incomplete at best. Two quarterbacks in particular became well known in both codes. Warren Moon, a California native who starred at the University of Washington, began his professional career with the Edmonton Eskimos before crossing the border back south to the Houston Oilers and later Minnesota Vikings, earning Hall of Fame recognition in both professional leagues. Doug Flutie, who authored a comeback win for Boston College considered an iconic moment in the history of American college football, began his professional football career in the USFL before moving on to the NFL, then played a long CFL career that led to him being the first non-Canadian honored with induction to Canada's Sports Hall of Fame, before returning to the NFL to close his football career. Dwayne Johnson played college football, and was on practice squad in the Canadian Football League. Ricky Williams played 12 seasons in the National Football