Hockey is Canada's national sport, although it's enjoyed in many countries. It's popular in Japan, Russia, the United States, and western Europe. Since 1920, hockey has been an official Olympic sport. Its roots have been traced to games of field hockey that British troops played on frozen lakes and ponds in Kingston, Ontario, and Halifax, Nova Scotia in the 1860s. In 1879, the first formal ice hockey rules were developed. Hockey is a rough, often brutal sport. Many injuries occur because of dangerous moves such as "body checking" (when a player throws his body against another to block his progress) and "poke checks" (when a player jabs opponents with his stick). In addition, the hockey puck can travel up to speeds of 115 miles (185 km) per hour.