Question: The 2006–07 Four Hills Tournament was a series of ski jumping competitions held in the traditional venues of Oberstdorf, Garmisch-Partenkirchen, Innsbruck and Bischofshofen, located in Germany and Austria, before the tournament started on which date, the World Cup leader was Simon Ammann, a Swiss ski jumper?
Context: The 2007–08 Four Hills Tournament was held in only three of the traditional venues of Oberstdorf, Garmisch-Partenkirchen and Bischofshofen, located in Germany and Austria.  The competition at Innsbruck was cancelled due to adverse weather conditions and replaced by an additional visit to Bischofshofen. Adam Henryk Małysz ( ; born 3 December 1977) is a Polish former ski jumper and rally driver.  He is one of the most successful athletes in the history of ski jumping, with his many accomplishments including 4 World Cup titles (a record shared with Matti Nykänen and Sara Takanashi), 4 individual Winter Olympic medals, 4 individual World Championship gold medals (an all-time record), 39 individual World Cup competition victories, a total of 96 World Cup podiums (individual and team), and being the only ski jumper to have won 3 consecutive World Cup titles.  He is also a winner of the Four Hills Tournament, and the only three-time winner of the Nordic Tournament. Sven Hannawald (born 9 November 1974) is a German former ski jumper, motor racing driver, and footballer.  In ski jumping he competed from 1992 to 2004, with his career best achievement being the winner of the 2002 Four Hills Tournament and becoming the only athlete in history to win all four events in the same tournament.  He also finished runner-up twice in the World Cup season, won four medals at the Ski Jumping World Championships, as well as three medals each at the Winter Olympics and Ski Flying World Championships.  After retiring from ski jumping, Hannawald played football for Kreisliga club TSV Burgau, and drove for Callaway Competition in the ADAC GT Masters series. Paul-Ausserleitner-Schanze ("Paul Ausserleitner Hill") was opened in 1941, and re-built in 2003, and is a ski jumping venue in Bischofshofen, Austria.  It is one of the more important venues in the FIS Ski jumping World Cup, annually hosting the fourth and final competition of the prestigious Four Hills Tournament.  It is named after Paul Ausserleitner, an Austrian ski jumper who died of the consequences of a fall on this hill in 1952. The Four Hills Tournament (German: "Vierschanzentournee" ) or the German-Austrian Ski Jumping Week (German: "Deutsch-Österreichische Skisprung-Woche" ) is a ski jumping event composed of four World Cup events and has taken place in Germany and Austria each year since 1952.  With a few exceptions the ski jumping events are held chronologically at Oberstdorf, Garmisch-Partenkirchen, Innsbruck and Bischofshofen. The 2006–07 Four Hills Tournament was a series of ski jumping competitions held in the traditional venues of Oberstdorf, Garmisch-Partenkirchen, Innsbruck and Bischofshofen, located in Germany and Austria.  The tournament was part of the 2006–07 Ski Jumping World Cup and points scored in each of the four competitions also counted towards the World Cup rankings.  Before the tournament started on 28 December 2006 the World Cup leader was Simon Ammann. Gregor Schlierenzauer (] ; born 7 January 1990) is an Austrian ski jumper.  He is one of the sport's most successful athletes of all time, having won the Ski Jumping World Cup, Four Hills Tournament, and Nordic Tournament twice each; the Ski Flying World Cup three times; as well as four medals at the Winter Olympics, five at the Ski Flying World Championships, and twelve at the Ski Jumping World Championships. Peter Prevc (] ; born 20 September 1992) is a Slovenian ski jumper.  He is one of the most successful contemporary athletes from Slovenia, having won the 2016 Ski Jumping World Cup, and finishing runner-up in 2014 and 2015.  His other accomplishments include winning the 2016 Four Hills Tournament; the 2016 Ski Flying World Championships; three consecutive Ski Flying World Cup titles (2014, 2015 and 2016); silver and bronze medals at the 2014 Winter Olympics; silver and bronze at the 2013 Ski Jumping World Championships; bronze at the 2014 Ski Flying World Championships; and bronze with the Slovenian national team at the 2011 Ski Jumping World Championships. The 2001–02 FIS Ski Jumping World Cup was the 23rd World Cup season of ski jumping.  It began on 23 November 2001 at Puijo in Kuopio, Finland, and finished on 24 March 2002 at Letalnica bratov Gorišek in Planica, Slovenia.  The defending World Cup champion from the previous season was Adam Małysz, who won the overall title for a second time.  Sven Hannawald placed second, as well as winning the Four Hills Tournament and becoming the only ski jumper in history to win the "grand slam" of all four competitions in the same event.  Matti Hautamäki finished third and won the Nordic Tournament.  The Nations Cup was won by Germany. Simon Ammann ( ; born 25 June 1981) is a Swiss ski jumper.  He is one of the most successful athletes in the history of the sport, having won four individual Winter Olympic gold medals, in 2002 and 2010, and is the only ski jumper to have achieved the gold double–double at the Winter Olympics.  Additionally he won the 2007 Ski Jumping World Championships; the 2010 Ski Flying World Championships; the 2010 Nordic Tournament; and the 2010 Ski Jumping World Cup.
Answer: 28 December 2006