Motocross is a form of motorcycle racing held on enclosed off road circuits. The sport evolved from motorcycle trials competitions held in the United Kingdom. Motocross is a physically demanding sport held in all weather conditions.

Motocross first evolved in the United Kingdom from motorcycle trials competitions, such as the Auto-Cycle Clubs's first quarterly trial in 1906 and the Scottish Six Days Trial that began in 1909. When delicate balancing and strict scoring of trials were dispensed with in favor of a race to be the fastest rider to the finish, it was called scrambles, said to have originated in the phrase, "a rare old scramble" describing one such early race. Originally known as scrambles racing in the United Kingdom, as the sport grew in popularity, the competitions became known internationally as motocross racing, by combining the French word for motorcycle, motocyclette, or moto for short, into a portmanteau with "cross country". The first known scramble race took place at Camberley, Surrey in 1924. During the 1930s, the sport grew in popularity, especially in Britain where teams from the Birmingham Small Arms Company (BSA), Norton, Matchless, Rudge, and AJS competed in the events. Off-road bikes from that era differed little from those used on the street. The intense competition over rugged terrain led to technical improvements in motorcycles. Rigid frames gave way to suspensions by the early 1930s, and swinging fork rear suspension appeared by the early 1950s, several years before it was incorporated on the majority of production street bikes. The period after World War II was dominated by BSA which had become the largest motorcycle company in the world. BSA riders dominated international competitions throughout the 1940s.