sweeper

A defensive position in football: “The sweeper’s job is mainly to play behind the defence to add extra security and improve the passing out of defence.”

Source: http://news.bbc.co.uk/sport2/hi/football/rules_and_equipment/4197172.stm

Football positions: http://news.bbc.co.uk/sport2/hi/football/rules_and_equipment/4196830.stm