The "audience wave" (also called a Mexican wave, or simply "the wave") is a phenomenon that commonly occurs in the audiences of sporting events, and sometimes in other large crowds. A wave is a coordinated sequence of actions taken by the audience members in which a group of spectators lying along a radial line extending outward from the sport field all stand up and raise their arms, then return to a normal seated posture again as the neighboring group of spectators takes their turn to stand up.
The result is a "wave" of standing audience members that travels rapidly through the audience, even though individual audience members never move from their seats (thus, the wave could be said to be a transverse wave). In many large arenas the audience is seated in a circular arrangement all the way around the sport field, and so the wave is able to travel continuously around the arena; in non-circular seating arrangements, the wave can instead reflect back and forth through the audience. When the gap in seating is narrow, the wave can sometimes pass through it. Usually only one wave crest will be present at any given time in an arena. Simultaneous, counter-rotating waves have been produced.
The exact origin of the wave is disputed. It first gained popularity in the United States in the early 1980s, with the Oakland Athletics baseball team reporting that the first appearance of the wave at a Major League Baseball game was led by professional cheerleader Krazy George Henderson in Oakland, California on October 15, 1981, in an American League Championship Series game against the New York Yankees. Others claim that the first wave originated in Seattle at the University of Washington's Husky Stadium on October 31, 1981, at the prompting of cheerleader (later Entertainment Tonight cohost) Robb Weller. The wave was apparently introduced into the soccer community at the 1986 World Cup in Mexico, from which the name "Mexican wave" derives. In Germany, Italy and other countries it's called "La ola" (Spanish for "The wave").
At the Sydney Olympic Games in 2000, the largest recorded wave, 110,000 people made an inverse Mexican wave and two simultaneous opposite direction waves
In 2002, Tamás Vicsek of the Eötvös University, Hungary along with his colleagues analyzed videos of 14 waves at large Mexican soccer stadiums, developing a standard model of audience wave behavior (published in the September 12 issue of Nature). He found that it takes only the actions of a few dozen fans to trigger a wave. Once started, it usually rolls in a clockwise direction at a rate of about 40 ft/s (12 m/s), or about 22 seats per second. At any given time an audience wave is about 15 seats wide. These observations appear to be applicable across different cultures and sports, though details may vary in individual cases.