Running is both a competition and a type of training for sports that have running or endurance components. As a sport, it is split into events divided by distance and sometimes includes permutations such as the obstacles in steeplechase and hurdles. Running races are contests to determine which of the competitors is able to run a certain distance in the shortest time. Today, competitive running events make up the core of the sport of athletics. Events are usually grouped into several classes, each requiring substantially different athletic strengths and involving different tactics, training methods, and types of competitors.
Running competitions have probably existed for most of humanity's history and were a key part of the ancient Olympic Games as well as the modern Olympics. Today, road racing is a popular sport among non-professional athletes, who included over 7.7 million people in America alone in 2002.
Wikipedia [accessed 10 May 2010] http://en.wikipedia.org/wiki/Long_distance_running#Running_as_a_sport