What are the most significant confirmed instances of match-rigging in football?

Question

What are the most significant confirmed (i.e. investigated by the governing body and punished) instances of match-rigging in football? When considering significance, please include:

• Level of the match: a World Cup match would be more significant than some Sunday morning pub football.
• Degree of match-rigging: arranging for a team to win is more significant than the time of the first throw-in.
• Effect of the match-rigging: something which enabled the team to win a league is more important than the difference between 12th and 13th place.
• Amount of match-rigging: more rigged matches is more significant.

Answer 1

There are definitely not as many match-fixing scandals in football as conspiracy theorists might have expected. Especially on such a high level, which your original question suggested.

One of the most popular match-fixing scandals that happened recently was Italian Calciopoli scandal, where many Serie A clubs were accused of rigging games by selecting favorable referees, during 2004/05 and 2005/06 seasons. As a result:

• Juventus was stripped of both 2004–05 and 2005–06 Serie A titles, was downgraded to 2006-07 Serie B while also receiving a handicap of starting with -9 points.
• Fiorentina was deducted 30 points from their 2005–06 Serie A run, making them finish 9th instead of 4th. Also received a handicap of starting with -15 points in the next season.
• Milan was deducted 30 points from 2005–06 Serie A, making them finish 3rd instead of 2nd. Received a handicap of -8 points in the next season.
• Lazio was deducted 30 points from 2005–06 Serie A, making them finish 16th instead of 6th. Received a handicap of -3 points in the next season.
• Reggina Received a handicap of -11 points in the next season.
• Siena Received a handicap of -1 point in the next season.

Here you can find a list of some minor match-fixing incidents in football most of which don't really meet the requirements of the edited question.

Answer 2

I think the Hoyzer Scandal is of enough significance.

The former referee Robert Hoyzer manipulated several matches in the German Cup (DFB-Pokal), 2. Bundesliga and Regionalliga. He was sentenced to serve 2 years and 5 months for match fixing in 6 cases.

List of matches he refereed:

DFB-Pokal:

• 21. August 2004: SC Paderborn 07 – Hamburger SV 4-2 (manipulated)
• 21. September 2004: 1. FC Nürnberg – LR Ahlen 2-3 (no proof of manipulation)

2. Bundesliga:

• 27. August 2004: Rot-Weiss Essen – Rot-Weiß Erfurt 0-0 (no proof)
• 26. September 2004: MSV Duisburg – SpVgg Greuther Fürth 1-0 (protest by Fürth and probably manipulated, but not enough proof)
• 22. October 2004: LR Ahlen – Wacker Burghausen 1-0 (manipulated and replayed)
• 28. November 2004: SpVgg Unterhaching – 1. FC Saarbrücken 1:3 (manipulation failed)

• And some Regionalliga matches

Answer 3

The most notable one is the 2006 scandal in the Serie A. Teams involved were Juve, Fiorentina, Milan and Lazio. Out of them, Juve were relegated to Serie B and stripped of their 2005 and 2006 Serie A titles. Many notable footballers like Zlatan Ibrahimovic, Gianluca Zambrotta, Patrick Vieira, Fabio Cannavaro left the club not wanting to play in a lower division. However, Players like Gigi Buffon, Alessandro Del Piero, Chiellini stayed loyal to the Old Lady. Even then Coach Fabio Capello left the Club.