High-profile incidents in 2019 brought the game into disrepute.new protocol, introduced in October, allows for the referee to abandon the match if racist behavior continues after two warnings issued by a stadium announcer.
Three stadium announcements that "racist behavior among supporters is interfering with the game" followed in the remaining half hour, a surreal, confusing and sad spectacle for soccer fans watching on television and in the stands.
"It is really sad to see racism again at a football match, but I think it's very important to talk about it in public," Rudiger posted on Twitter after the incident. "If not, it will be forgotten again in a couple of days (as always)… When will this nonsense stop?"
Eventually, Tottenham and the police said they could find no evidence that Rudiger had been subjected to the taunts -- although a Chelsea fan was arrested for racially abusing a Tottenham player, Son-Heung-Min. Chelsea has not commented.
The incident closed out a year in which levels of racism in European soccer, described by anti-racism advocates as an "epidemic," reached new heights.
Year of shame
If this was the first time the new protocol had been used, it certainly doesn't look like it will be the last. Over the course of the 2018-19 season, which ran from September to July, England's anti-racism and pro-inclusion group for the sport, Kick It Out, released statistics demonstrating that reports of discrimination, on the grounds of gender, sexual orientation, religion and race, had increased 32% from the previous season -- from 319 to 422.
Racist incidents constituted 65% of those reports, the data shows.
The problem hasn't just been racist abuse directed at players. Alongside racist incidents, anti-racism charities have long criticized soccer's governing bodies for limp responses to these incidents and weak punishments, paying lip service to problems without showing leadership in stamping them out. Both FIFA, the world's soccer governing body, and UEFA have pushed back on those assertions, blaming the rise of nationalism and reaffirming their own commitments to fighting racism.
"UEFA's sanctions are among the toughest in sport for clubs and associations whose supporters are racist at our matches," the organization said in a statement in October.
Among the highest profile incidents was a match between England and Bulgaria in October, which saw Bulgaria supporters allegedly directing Nazi salutes and monkey chants at England's black players, forcing the game to stop twice. Bulgaria already was halfway through a partial stadium ban for previous racist incidents, which saw 5,000 fans blocked from entering a 46,000-seat stadium in October.
Kick It Out issued a statement saying it was "sickened" by the incident, and that serious action was needed in order to tackle such discrimination.
After the match, the president of the Bulgaria Football Union resigned "as a consequence" of the "tensions" surrounding the match, although the organization did not specifically mention racism in its statement.
UEFA fined the Bulgarian soccer association $83,000, and hit the team with a two-game stadium closure, meaning no fans were allowed in to watch those matches.
Iffy Onuora, the equalities coach for the Professional Footballers' Association, the trade union for soccer players in England and Wales, told ABC News that that match, given what he described as Bulgarian soccer's history of racism, was a "seminal moment in recent years."
"How did that happen when it was widely anticipated?" he said. "I think the profile of the game, an England international [match] involving the very best players in the country, I think that's when it really threw everything into sharper focus."
Perhaps the best example on the European continent of the failure of institutions to tackle the problem was in fact an anti-racism campaign in Italy, considered by many to be historically one of the worst offenders.
The "No-to-Racism" posters, officially sanctioned by Serie A, Italy's top league, featured images of monkeys' faces and were displayed at Serie A headquarters in Milan in a December presentation. Serie A eventually apologized after a public backlash, as just a month earlier the Italian striker Mario Balotelli was left visibly distraught on the field after being subjected to monkey chants in a match against Hellas Verona.
Christos Kassimeris, a professor of political science at the European University Cyprus who is authoring an upcoming book titled "Discrimination in Football: isms and phobias," told ABC News that the incident "speaks volumes of the kind of ignorance that best describes many" across the continent.
"Simply put, acknowledging that racism in football exists is certainly not enough to either support football players or equip them with the necessary tools that would enable them to make a difference," Kassimeris said.
Piara Power, executive director of Football Against Racism in Europe, an anti-racism umbrella group that includes supporters' groups and NGOs, told ABC News that the Italian example was particularly bad although some problems are common across the continent.
"There's no question that mimicry is part of this -- people see it happening in one part of Europe and think that's a good thing to do," Power said. "That reflects the demographic of individuals involved, often young men who will follow and copy each other."
Soccer 'mirrors society at large'
Yet soccer, by far the world's most played and watched sport, does not exist in a bubble. Indeed, the first point many anti-racism campaigners point to in discussing the issue is the political developments that have emerged in Europe since around 2015. The "epidemic" of racism is impossible to understand without grasping the continent's shifting politics, according to Power.
"People are now saying things that perhaps even five years ago they would have hesitated to say in a public space," he told ABC News. "Across Eastern Europe you can look at Hungary, Poland, Slovakia -- where populist governments have a far-right agenda. They are often using language of intolerance, scapegoating minority communities. A lot of this is spilling over into football."
Onuoura, who's black and whose playing career spanned the entire 1990s in England's lower divisions, is as well-placed as any to have observed how the game has changed. Black players came to prominence in the U.K. in the 1970s, and racism was widespread in the game, which continued into the next decade, he said, but his days as a professional were "a period of calm."
"The direction ... was definitely to more tolerance, more inclusion, to try and improve situations for minority people in this country," he told ABC News. "I'm not sure that direction has carried on in the same way. If you accept it or don't accept it, what you can say with a reasonable degree of certainty is football is a reflection of society. Football doesn't exist in a vacuum."
The political climate, as well as the "perfect storm" of social media allowing fans to anonymously abuse players, has spilled out into modern soccer, Onuoura said. Several high-profile players and coaches have called on social media companies to do more to stamp out racist abuse online.
"The game of football mirrors society at large," Kassimeris said. "With the British prime minister, Boris Johnson, comparing women in burkas to 'letterboxes' or the Hungarian prime minister, Viktor Orban, often expressing his xenophobic views, racism in European politics is reaching unparalleled heights."
Johnson refused to apologize for his remark, calling it a "strong liberal defense ... of everybody's right to wear whatever he wants in this country." Orban, meanwhile, has rejected criticism that he is racist, which came from the UN High Commissioner on Human Rights.
A Kaepernick effect?
Indeed, it was frustration with how much of the tabloid press treated black soccer players in the U.K. that appears to have sparked another watershed moment in how racism in soccer is perceived -- the closest the game has come to a "Colin Kaepernick" moment.
Manchester City player Raheem Sterling, who is black, issued a statement on Instagram. Sterling, who's regularly been targeted on the field, and criticized by the media, called out the tabloid media's coverage of two young soccer players buying houses for their mothers -- one black, and one white.
His teammate, Tosin Adarabioyo, who is black, was criticized in reports in the MailOnline for buying a house for this mom, while white teammate Phil Foden also bought a lavish house for his mother but did not appear to receive the same criticism. Sterling himself had been criticized for buying a house for his mom by the MailOnline in 2017, with the headline "£180,000-a-week England flop Raheem shows off blinging house he bought for his mum -- complete with jewel-encrusted bathroom -- hours after flying home in disgrace from Euro 2016."
"This young black kid is looked at in a bad light," Sterling's statement read. "Which helps fuel racism an[d] aggressive behaviour, so for all the news papers [sic] that don't understand why people are racist in this day and age all I have to say is have a second thought about fair publicity an[d] give all players an equal chance."
The reporter on the story denied that the piece was about race and tweeted that "it didn't even cross my mind."
"We are now seeing a cohort of players who feel like they have the agency and capability to challenge racism in ways that haven't been done before," Daniel Burdsey, a sociologist at the University of Brighton who researches racism in sport and society, told ABC News.
As of November last year, there were only six black, Asian or minority ethnic, or BAME, managers out of the 72 teams in the top four divisions of English soccer. A report released last year by the FA, U.K. soccer's governing body, found that people from BAME backgrounds make up only 6% of "leadership roles" in the sport in England and Wales.
Meanwhile, only 4% of referees identify as BAME, according to the FA.
"We hear racism being shouted on the terraces, but it also happens when a black official walks up to a boardroom [of a soccer club], but doesn't get recognized as an official, because the person upstairs doesn't recognize him and ... I've experienced some of that myself," Onuoura told ABC News. "There's the culture of 'black players play,' and non-black players coach, manage, lead and are senior management in the company."
The U.K.'s governing institutions have implemented the NFL's so-called Rooney Rule, whereby clubs must interview at least one BAME candidate for management positions, but the problem, for campaigners inside the game, goes far wider than that, and the solutions are far from clear.
"Football can do better," Onuoura said. "[But] we've allowed the narrowing of opinion, the shutting down of opinion, this intolerance to seep into our culture over the last eight to 10 years ... and it might take another eight to 10 years to turn that the other way."
ABC News' Eden McClymont and Samee Macarthur-Caffoor contributed to this report.