On 6 May 2010 Peruvian side Alianza Lima travelled to Chile to face Universidad de Chile in the last 16 of the Copa Libertadores. They were 0-1 down from their home leg but had established a 1-2 lead going into injury time at the end of the game and looked set to progess to the quarter finals on goal difference.
When Felipe Seymour fired in a long range shot, the goal looked set to be disallowed as the linesman was flagging, however the referee overruled him and awarded the goal anyway. In retrospect it looks like a poor decision, there was an offside in the build up play and two Universidad de Chile players were offside and in the goalkeeper's line of sight when the shot came in.
The Alianza Lima players and staff were understandably upset and surrounded the referee to complain prompting the Chilean police to come onto the pitch in scenes reminiscent of scenes in the Copa Libertadores semi-final in the same stadium back in 1991 when the Chilean police set about intimidating the Boca Juniors players with dogs instead of clearing the pitch invasion by hundreds of Colo-Colo fans.
For more crazy South American football check out the rest of the Cosas locas series.