The most controversial sport on the planet is probably soccer, due to its match-fixing scandals, erratic refereeing, and unsavory hooligan elements. Controversy and soccer have gone hand-in-hand for decades and unfortunately the UEFA Champions League is no exception. There have been numerous debatable referee and player decisions since the league’s current inception in 1992-93, and we’ll feature 12 of the most memorable here.

This list deals with the most controversial moments of the Champions League with most of them being the result of refereeing calls or non calls. There are a few exceptions, but overall these are the dozen moments that usually ignite highly-emotional debates between various sets of fans. Compared to some of these instances, this year’s tournament has been relatively controversy-free so far.

12. Luiz Adriano’s Unsportsmanlike Goal

All’s fair in love and war, but apparently not in soccer. In November 2012, Shakhtar Donetsk was playing Danish minnows Nordsjaelland away and found themselves trailing 1-0 after 24 minutes. Shortly after, play was halted due to a collision and injury to a Nordsjaelland player. The game was restarted with a drop ball, but no Nordsjaelland player contested it, just Willian of Donetsk.

He booted it downfield towards the opposing goalkeeper to give them possession of the ball. Donetsk’s Luiz Adriano intercepted it though and went in alone on the keeper, who didn’t attempt a save, and scored. It was a legal goal at best and unsportsmanlike at worst. Nordsjaelland tied the game 2-2 just a few minutes later, but Adriano ended up with a hat trick in a 5-2 win for Donetsk. UEFA later suspended Adriano for a game for unsportsmanlike play and his manager Mircea Lucescu made a public apology.

11. Robin van Persie’s Red Card vs Barcelona

Arsenal was playing Barcelona at Camp Nou in the second leg of a Round of 16 clash back in March 2011 and were ahead 3-2 on aggregate. Early in the second half, Arsenal’s leading scorer Robin van Persie broke toward the goal and unleashed a shot which found the back of the net. However, referee Massimo Busacca ruled he was offside. That wasn’t the end of it though as he then produced a yellow card to Van Persie and the Dutchman was sent off since it was his second of the game. The player strongly argued the call by saying he never heard the whistle due to the deafening noise of the 90,000 fans inside the stadium. The obvious happened next, as Barcelona scored twice with the man advantage to advance. After the game, television replays showed Van Persie took his shot just one second after the whistle had blown.

10. Nani’s High Boot Results in Red Card and Defeat

Manchester United had a 2-1 aggregate lead over Real Madrid in the quarterfinals back in March 2013 and were playing at Old Trafford in the second leg. In the 56th minute, United’s Portuguese international Nani caught Alvaro Arbeola with a seemingly unintentional high kick and was promptly sent off by referee Cuneyt Cakir. Once again the inevitable happened, as Luka Modric and Cristiano Ronaldo both scored against their 10-man opponents and advanced to the semifinals. United argued that Nani was attempting to play the ball, but the referee insisted a high boot was a dangerous play, no matter if it was intentional or not — following the letter of the law quite literally. Understandably, Cakir felt he was justified in sending Nani to the showers, but United fans obviously didn’t see it that way. Then-Madrid manager Jose Mourinho even remarked after the game that his team probably didn’t deserve to win, but caught a lucky break.

9. Barcelona Eliminates AC Milan After Controversial Penalty

As with all the top teams, Barcelona often benefits from dubious penalty calls from game officials (leading to tongue-in-cheek nickname UEFAelona). One example took place in the quarterfinals at home against AC Milan in April 2012. The first leg in Italy ended 0-0 and the second match was 1-1, with Barcelona’s goal coming on a cut and dry penalty after Lionel Messi was brought down in the box.

Barcelona was then awarded a second penalty in the 41st minute by referee Bjorn Kuipers. He blew the whistle just as Barcelona was about to take a corner kick and claimed Alessandro Nesta had wrestled Sergio Busquets to the ground. Milan players complained that Barca skipper Carles Puyol was actually the one to blame, as he was interfering with Nesta. Milan also pointed out that Kuipers had awarded the penalty before the ball was in play from the corner and therefore wasn’t a legitimate call. Messi slotted it home anyway and Barcelona went on to win the match and tie 3-1.

8. Celtic gets Second Chance as Legia Warsaw Uses Ineligible Player

Polish side Legia Warsaw didn’t have much trouble disposing of Celtic in August 2014, as they trounced the Scottish side 6-1 on aggregate in the third qualifying round. But with Warsaw in command, Bartosz Bereszynski was sent on the pitch as a late substitute in the second leg. Celtic protested his presence and it turned out to be a great move, since UEFA ruled Bereszynski was an ineligible player after receiving a red card the previous season and wasn’t registered to play.

The Glasgow team was then handed a 3-0 victory by default. Since they lost the first leg 4-1 away, the score was now 4-4 on aggregate and Celtic advanced due to their away goal. Legia appealed the decision, but it was upheld. Celtic didn’t take advantage of their reprieve as minnows Maribor of Slovenia knocked them out in the playoff round.

7. Sergio Busquets Takes a Dive

Barcelona’s Sergio Busquets enraged Inter Milan fans during the 2010 Champions League semifinals for taking a dive. Inter won the first leg 3-1 at home and things weren’t looking too good for Barcelona in the return match either. Busquets tried to turn his team’s luck when Thiago Motta’s hand struck his face during a race for the ball and he fell to the ground like he’d been struck by lightning.

The cameras remained on Busquets and caught him moving a hand away from his eyes to see if referee Franck De Bleeckere was going to hand Motta a red card. Motta was already on a yellow and was indeed sent off the pitch for a second bookable offense — and it was only the 28th minute. Barcelona managed to score against 10 men, but the Italian side hung on for a 3-2 aggregate victory and went on to win it the European Cup that year. This was aided in part by referee De Bleeckere, as he disallowed a Barcelona goal later in the game. Perhaps it was a make-up call?

6. Luis Garcia’s “Goal” Against Chelsea

Unfortunately for Chelsea there wasn’t any goal line technology in use back in 2005. The Blues were playing the Reds from Liverpool in the semifinals and the first leg ended 0-0 at Stamford Bridge in London. Shortly after the second leg kicked off at Anfield, Liverpool’s Luis Garcia was awarded with a goal even though the ball it didn’t appear to fully cross the line. Instead, most observers felt Chelsea defender William Gallas managed to clear the ball before it had a chance to cross the line.

Referee Lubos Michel of Slovakia was the man in charge though, and much to the delight of Liverpool fans (and the dismay of Chelsea supporters) he awarded a goal. Chelsea manager Jose Mourinho called it the “ghost goal” and it just happened to be the only one of the game. Liverpool advanced and famously came back from a 3-0 deficit in the final to snatch the trophy away from AC Milan.

5. Chelsea vs Barcelona Part 1 – Missed Penalty Calls

Arguably, the most controversial match in Champions League history was the second leg of the May 2009 semifinal between Barcelona and Chelsea at London’s Stamford Bridge. Chelsea had escaped the first leg at Camp Nou with a 0-0 draw and were in front 1-0 at home, courtesy of a Michael Essien goal. The home side created more chances and ended up with four legitimate appeals for penalties, but referee Tom Henning Ovrebo of Norway waved all of them off.

He did do Chelsea a favor though, as he sent Eric Abidal off in the 66th minute. Chelsea felt they deserved two penalties for apparent handballs and another two for fouls inside the box, but Ovrebo ignored them all. Andres Iniesta then scored in the third minute of injury time to send Barca through on away goals. What happened next deserves its own entry on this list…

4. Chelsea vs Barcelona Part 2 – Drogba Loses It

Let’s stay with the Barcelona vs Chelsea saga. Chelsea fans accused UEFA of fixing the semifinal tie as they didn’t want two English teams in the final again. Manchester United had already qualified for the 2009 championship game and a Chelsea win would have meant the same two teams would be battling it out for the second straight year. Iniesta’s last-gasp goal definitely got Chelsea’s blood boiling and this caused their Ivory Coast international striker Didier Drogba to lose it.

He chased after referee Ovrebo and got in his face as he tried to enter the tunnel. Several of Drogba’s teammates and a couple of stewards tried to control him, but he broke loose and shared his feelings with the world by yelling into a nearby camera, including a well timed expletive (“It’s a f**king disgrace!”). Drogba was banned for six European games due to his actions with two of them being repealed, meaning he missed four matches.

3. Chelsea vs Barcelona Part 3 – Referee Admits Mistakes

The epilogue of the Barcelona vs. Chelsea soap opera saw Didier Drogba banned for four games and his teammate Jose Bosingwa suspended for three. Bosingwa apparently called referee Tom Henning Ovrebo a thief after the game and Chelsea was fined €100,000 as their fans threw objects on the pitch after the final whistle. As for Ovrebo, unfortunately he received several death threats via social media, with some fans going as far as creating a Kill Tom Henning Ovrebo page on Facebook.

The referee later admitted to making several mistakes during the crucial second leg of the semifinal. It wasn’t long after that he was NOT invited to work the 2010 World Cup in South Africa and he promptly resigned from working international games. Nobody knows if Chelsea would have converted any of the missed penalty calls, but at least they would have had the chance if Ovrebo didn’t have a brutal day at the office.

2. Referee Anders Frisk Quits After Death Threats

Interestingly enough, the Barcelona vs. Chelsea controversy involving referee Ovrebo wasn’t the first disputed Champions League match between the teams. They also caused a ruckus in 2005 when they met in the Round of 16 with Jose Mourinho in charge at Chelsea. The first leg was held at Camp Nou and Swedish referee Anders Frisk handed Chelsea’s Didier Drogba a second yellow card in the 55th minute when he collided with the goalkeeper.

Chelsea was leading 1-0 at the time and would go on to lose 2-1. Mourinho wasn’t happy and let the press know that Barcelona manager Frank Rijkaard had visited Frisk in the referee’s room at half time before Drogba was dismissed. Frisk, an insurance agent, received numerous death threats from English fans and shocked the football world by announcing his retirement just a couple of weeks later. Chelsea ended up advancing with a 4-2 win and Mourinho was banned from the touchline for the quarterfinals round.

1. Marseille Booted out of 1993-94 Champions League

The only French team to win the Champions League has been Olympique Marseille, as they hoisted the trophy in 1993, the first of the Champions League era. It didn’t come without controversy though. Marseille was scheduled to meet Valenciennes in a French league match a few days before taking on AC Milan in the final in Munich. Marseille club president Bernard Tapie asked one of his players to speak with members of Valenciennes and suggest they take it easy against his side before the final and let Marseille win.

The news of this (and other match-fixing instances) eventually found the light of day. The French league title was stripped from Marseille. In addition, the club was banned from top European competition in 1993-94, relegated to the French second division, and Tapie was banned domestically for life. They were allowed to keep their Champions League crown though.