There are 4 main versions of Gridiron Football: the traditional 11v11 game played in USA, a 12v12 version of the game played in Canada, and a 8v8 version of the game played Indoors on converted Ice Hockey Arenas.
 Professional Football Researchers Association (2011) “No Christian End!” The Early History of Professional Football. pg. 23-32. PFRA Publications. Connecticut.
Irish-Born Canadian Football Players
With the first tour of Ireland and Britain in 1994 Canadian teams have been playing Irish teams at American Football, with Canadian rules thrown in.
Canadian Football League Major Era 1956-Present
The 12v12 version of the game played in Canada differs from American Football not only in the number of players allowed on the field at any one time (12 in a Canadian Football team versus 11 in an American Football team), but also in the size of the field (a Canadian Football field is 110 yards long with two 20-yard endzones, while an American Football field is 100 yards long with two 15 yard endzones). Canadian Football teams also have only three downs (attempts) in which to gain 10 yards or the ball is turned over as opposed to four downs in American Football. There is also the possibility of scoring a “Rouge” in Canadian Football – this happens when the ball is kicked through the back of the endzone, and is worth one point.