Its actually a rule in Football (socccer). Basically it  is designed to stop players hanging around the goal! A player is offside if he is nearer to his opponents' goal line than both the ball and the second last opponent, unless he is in his own half of the field of play. Recently the rule has changed to be only active players, causing much controversy!\nCheck out the BBC site here:\nhttp://news.bbc.co.uk/sport1/hi/football/rules_and_equipment/default.stm\n\nOffside rule:\nhttp://news.bbc.co.uk/sport1/hi/football/4679881.stm