The rules of baseball differ slightly from league to league, but in general share the same basic game play. Rules There are several major rules, which differ only slightly. The "Official Baseball Rules" govern all professional play in the United States and Canada, including the World Baseball Classic. The complete rules are published as the Official Baseball Rules at MLB.com, the official web site of Major League Baseball in the United States and Canada. The rules are also published in book form in North America by the Sporting News. Many amateur and youth leagues use the "OBR" with only a few modifications for safety. Other slightly modified versions of the "Official Baseball Rules" are used in competitions operated by the World Baseball Softball Confederation (WBSC), including the Olympics, World Cup, and WBSC Premier 12, most leagues outside North America (such as Japan's Nippon Professional Baseball), and youth baseball organizations such as Little League, PONY League, and Cal Ripken League. The baseball rulebook of the National Collegiate Athletic Association (NCAA), aside from governing the games of that organization's members, is also used by several other competitions involving college-aged players. U.S. high school and high school-age baseball is governed by the rules of the National Federation of State High School Associations (NFHS). Differences and evolution For the origins of the game, see Origins of baseball. Unlike many other sports, the Official Baseball Rules have remained mainly static during the modern era of the game. Many baseball players, fans, and administrators view the rules and traditions of professional baseball as time-tested and nearly sacrosanct. This was not the case during baseball's early days, particularly in the late 19th century, when rules were changed significantly and often yearly. The game as we know it today really began to take shape only in the late 1880s, and even after that, many significant rule changes were made during the rest of that century. In 1857, under the NABBP Rules which governed until 1870, the current 9-inning format was adopted, replacing the previous rule that the first team to score 21 runs won. The next year called strikes were recognized, and a batter was out if a ball, fair or foul, was caught on the fly or after one bounce. Called balls and the walk were introduced in 1863. In 1867, the batter had the right to call for a high or low pitch, to be determined