10 August 1984
Zola Budd and Mary Decker are athletes who took part in the 1984 Los Angeles Olympics. Budd, a South African, was competing under British citizenship due to apartheid laws in South Africa, and Decker,was representing the US. Both athletes were to compete in the 3000m race, with Decker being the favorite to win. During the race, Budd accidently tripped Decker and the American fell off the tracks. She injured her hip and was unable to continue with the race.  The crowd expressed their anger by booing Budd, who continued on to finish seventh. Budd later claimed to have thrown the race in order to avoid further booing from the crowd had she won.  The incident is regarded as one of the biggest upsets in Olympics history.
References

Trackandfield Did Zola Budd Trip Mary Decker? Olympic Distance Running Controversy[online] Available at: https://trackandfield.about.com[Accessed on 16 July 2012]|ESPN Budd & Decker clash in explosive final[online] Available at: www.espn.co.uk[Accessed on 16 July 2012]