Canadian Football League (CFL) between 1997 and 2008. Many, if perhaps not most, of the rules differences have arisen because of rules changes in American football in the early 20th century, which have not been copied by Canadian football. The major Canadian codes never abolished the onside scrimmage kick (see Kicker advancing the ball below) or restricted backfield motion, while the American college football (from whose code all American codes derive) did. Canadian football was later in adopting the hand snap and the forward pass, although one would not suspect the latter from play today. Additionally, Canadian football was slower in removing restrictions on blocking, but caught up by the 1970s so that no significant differences remain today. Similarly, differences in scoring (the Canadian game valuing touchdowns less) opened up from the late 19th century, but were erased by the 1950s. An area in which American football has been more conservative is the retention of the fair catch (see below). The American game's modern rules were developed by Walter Camp in the late 19th and early 20th centuries, whereas the modern Canadian game was devised by John Thrift Meldrum Burnside, whose Burnside rules, invented around the same time, were developed independently from Camp's rules. In some regions along the Canada-U.S. border, especially western areas, some high schools from opposite sides of the border regularly play games against one another (typically one or two per team per season). By agreement between the governing bodies involved, the field of the home team is considered a legal field, although it is a different size from one school's normal field. In all but a few cases, the rules of the home team are followed throughout the game. Many CFL players are Americans who grew up playing American football and cannot find a place in the NFL, or who prefer to play in the CFL; strict import quotas restrict the number of non-Canadian players. Furthermore, the classifications of import (non-Canadian) and non-import (Canadian) were highly restrictive and required a player to have been in Canada since childhood to qualify as a nonimport (i.e. a player cannot simply become a Canadian citizen and become a nonimport, nor can he arrive in Canada during high school or college; both scenarios would still have the player in question classified as an import and counted against the team's maximum); these restrictions were loosened beginning in 2014 so that anyone