Speed skydiving is an extreme sport that requires practicians to jump out of an airplane and try to reach and maintain the highest possible terminal velocity.
Invented in the late 1990s, speed skydiving is recognized as the fastest non-motorized sport on Earth. Competitions begin with skydivers jumping out of an airplane between 13,000ft and 14,000ft (3,962m to 4,267m), then turning 90° from the direction in which the aircraft is traveling, alternately left and right. Next, competitors go into free fall head-first towards the earth, while trying to be as aerodynamic as possible. It is within this stage that they reach the highest speeds. Depending on a variety of factors, including body mass, orientation, and weather conditions, competitors can reach speeds of over 500 km/h (310 mph).
Source: ODDITYCENTRAL