Hopp (centre) has put an estimated 350m euros (£301m) into his hometown club

The rain was pouring hard as Bayern Munich midfielders Leon Goretzka and Joshua Kimmich did keepie-ups with Sebastian Rudy of Hoffenheim in the centre circle.

Thiago, also in Munich red, joined in too, and before long the two opposing sides were casually passing the ball back and forth between them.

At first glance, it looked like a 13-minute training session in front of 30,000 spectators. But this was a Bundesliga game that for the first 77 minutes had only been about Bayern's dominance. They had a clear 6-0 lead when something happened that is unprecedented in the long history of German football.

It started with banners in the away end housing Bayern supporters. One read "Du Hurensohn" ("You son of a whore") with the letters D and H coloured in blue. It was quite clear who this was aimed at - Hoffenheim's main financial backer, Dietmar Hopp.

The 79-year old was watching from the VIP stand with a bewildered look on his face as Bayern's chief executive Karl-Heinz Rummenigge ostentatiously put an arm around his shoulder for comfort. The referee stopped the game - there had been instructions to do so should insults be displayed on banners or voiced from the crowd.

Bayern manager Hansi Flick, and sporting director Hasan Salihamidzic then sprinted to the away supporters, shaking their heads, waving their hands and holding up six fingers to show the score. In their eyes, the fans were putting the result in jeopardy. The supporters might have replied that their concerns were worth more than three points.

Bayern's players followed, vainly attempting to speak with ultras in the first few rows. Then the referee pointed to the tunnel to send the players off the pitch.

Visiting captain Manuel Neuer spoke with Hoffenheim's players and their manager to discuss the idea of a strike during the remaining 13 minutes. When the players returned to the pitch, Hoffenheim's supporters booed their decision. They wanted the game to be cancelled.

Rummenigge and Hopp arrived on the touchline holding hands in an act of solidarity. After the game, both teams applauded the crowd - apart from the Bayern section - and they let Hopp stand in the middle.

Hoffenheim have an average attendance of 26,836 this season - 89% of their capacity. Four Bundesliga clubs have a lower percentage - Wolfsburg, Mainz, Fortuna Dusseldorf and Hertha Berlin.

Rummenigge spoke. "This was the ugly face of the football and of Bayern Munich."

Tabloid media headlines read: "A day of shame for German football." During Aktuelles Sportstudio, a TV programme like Match of the Day, highlights of the match were shown in silence - with no commentary on the action.

German football has since been occupied by the aftermath of this match. It has divided the game. Do you sympathise with the anger of the supporters? Or do they have too much power? Do you support the football authorities? Or do you believe they are guilty of hypocrisy?

Many people are asking where German football is heading. But to understand the origins of this conflict, you have to look back and consider more closely Hoffenheim's divisive owner, the man at the centre of a complex set of circumstances that has been building up over the past decade at least.

Hopp made his fortune in IT. He founded the company SAP in the 1970s and became a multi-billionaire. He has supported projects for protecting the environment and donated hundreds of millions towards education, children's projects and medical research. It is a feature that supporters - including Rummenigge - are keen to highlight, and even his critics will not denounce. But Hopp's critics see his private benevolence as irrelevant to football. They are more interested in his role as an investor and patron of TSG Hoffenheim.

Since the late 1980s, Hopp has put a large amount of money into his hometown club. The sum of his investment is believed to be about 350m euros (£301m).

The Dietmar Hopp Stadion was Hoffenheim's home until 2009, when they moved to the 30,000 capacity Rhein-Neckar-Arena in Sinsheim

With the help of his money and the skills of manager Ralf Rangnick, the 'village club' climbed from the sixth tier to the top within 10 years, securing Bundesliga promotion in 2008 and sitting top of the table halfway through their maiden season. The team, representing a village of 3,000 inhabitants, made it through to the Champions League group stages for the first time last season.

The story of an owner pushing his childhood club to the top might sound like a fairytale. It was presented this way in most of the German media back in 2008. But many supporters, especially many ultra groups, felt angry that an exception had been made to accommodate Hopp and his big spending.

Because of Germany's 50+1 rule, commercial interests or individuals are not supposed to gain full control of a team. Club members are supposed to at least own more than half the shares - 50% of the deciding votes, plus one more.

But football's governing body in Germany (DFB) had already softened this rule in a move known as 'Lex Leverkusen'. Bayer Leverkusen do not strictly adhere to 50+1, because of links to the Bayer pharmaceutical company. But they were founded by factory workers and have built their position through a long history of success on the pitch. VFL Wolfsburg have a similar background - the old factory team of Volkswagen.

'Lex Leverkusen' allows scope for investors who have been funding the parent club "continuously and substantially" for more than 20 years to bypass the 50+1 regulations. This was the case for Hopp. It gave him the right to take over majority ownership of Hoffenheim while, officially, sticking to the rules.

But the idea behind 50+1 - to avoid clubs having a strong financial dependence on an investor, and to protect them from the consequences of that dependence falling through - was in many people's eyes undermined. Hoffenheim is Hopp. The club wouldn't be anywhere near the top flight without his support.

From the beginning, ultra groups have considered Hopp a symbol for the commercialisation of the game. They believe that his financially powerful and privileged club is stealing the place of another with more restricted means. Several officials from top-flight sides, such as Mainz or Dortmund, have shared similar opinions in interviews.

In the stadiums, that criticism has turned vitriolic. Fans have for years chanted insulting slogans during games, and the protests went further still when Dortmund ultras displayed a banner with Hopp in a crosshairs with the message "Hasta la vista" in 2008.

Hoffenheim celebrate winning promotion to the Bundesliga in 2008 - their team that year included Demba Ba, who left to join West Ham United in 2011

Three years later, a Hoffenheim employee admitted to having used a sound machine to drown out Dortmund's away fans' chants in their stadium. This incident led to the song pun "Du Sohn einer Hupe" ("you son of a horn"). Hopp apologised in a letter but added: "The ones who insult me for 90 minutes shouldn't be too sensitive."

His words sparked more anger, and the situation worsened when Hopp instructed club staff to put microphones in front of away fans to record any insults. In 2019, he took Dortmund and Cologne supporters to court, and some were fined for their behaviour towards him.

Meanwhile, the DFB declared that Dortmund fans were on probation for their next away game at Hoffenheim. The Dortmund fans knew what was coming when, during their match there in December 2019, they sang "never again Hoffenheim" and once more displayed insulting banners.

All Dortmund fans were banned from the next two matches at Hoffenheim. It represented a return to collective punishment - something that the DFB and its then-president Reinhard Grindel had promised to abolish in 2017. Now there was a new factor in fans' opposition to Hopp, the starting point for a new wave of criticism focused on him.

Even ultras of Borussia Monchengladbach, who have a very tense relationship with Dortmund ultras, showed support for their rivals. In February this year, they raised the same banner as Dortmund ultras had, with Hopp in the crosshairs. Only a few days before, on 19 February, a gunman had killed nine people in the German city of Hanau.

Gladbach officials criticised their ultras and apologised to Hopp. During the fallout, some commentators and officials went as far as placing the banner on the same level as the murders. It was a trivialisation of the shocking events in Hanau, but it set the tone for what was to follow during the next week, and it led to strong decisions at the DFB.

Dortmund's fans display banners depicting Hopp (centre), his lawyer Christoph Schickhardt (second left), Fritz Keller (second right), German FA vice-president Rainer Koch (left) and Bayern Munich chief executive Karl-Heinz Rummenigge (right), in March 2020

Murder, racism, insults, discrimination - all these themes mixed together in the public debate. So when word spread that more fan groups would protest against Hopp the next weekend, the DFB decided to apply the three-step-protocol originally set up by Uefa to combat racial abuse. When there was any discrimination, step one would see the game halted and an announcement made. Step two would be to take teams off the pitch, with a second announcement. Step three would see the match abandoned.

This led to the events we saw at the end of Hoffenheim's match against Bayern. But that wasn't the only fixture to be interrupted. In Cologne, Berlin, Dortmund and elsewhere in lower divisions, matches were stopped when the referees noticed banners in the stands.

The main problem was that there was little time for the referee to carefully read, and often put into context, what was actually written on the banners. During the game in the third division between Meppen and Duisburg one series of banners read: "If Dietmar has enough cash, for his protection and interest, people whose words are meaningless will lock someone up again."

Even Duisburg's press co-ordinator said he had no clue why the game was interrupted, because the statement of the banner should be covered by freedom of speech.

There were new questions emerging. At what point is the referee to implement the three-step plan? And how could they be expected to track action in the stands while simultaneously officiating a busy football match? These and other questions were sent to the football association by clubs from the second division- but without any satisfactory answer.

This inconsistency of the DFB came to the foreground when Schalke played Bayern three days after the 'strike' in Hoffenheim.

While Bayern fans insulting Hopp had led to an interruption there, nothing happened when Bayern goalkeeper Manuel Neuer was insulted with the same phrase by Schalke supporters.

RB Leipzig's Timo Werner has been similarly abused in nearly every stadium in the country after a perceived dive, and various fan groups suffer the same in many infamous chants, including one particularly insulting song delivered by Hoffenheim supporters to fans of Freiburg.

But what infuriated supporters in Germany most of all was the lack of action over racist insults. During the game between Schalke and Hertha Berlin a few weeks before the escalation surrounding Hopp, Hertha defender Jordan Torunarigha was racially abused from the stands without an interruption or announcement in the stadium.

When midfielder Mesut Ozil was the target of racist comments from far right politicians during the World Cup 2018, the DFB admitted taking too long to defend him. external-link These cases led to the suspicion that German football does more to protect multi-millionaires than it does minorities, or players with a migrant background. The atmosphere of double standards is fostered by the long-term "co-innovation partnership" external-link between Hopp's company SAP and the DFB. SAP will also sponsor the future home of Bayern Munich's basketball team.

A pamphlet produced by Paderborn fans explains their stance on the 'Hopp Cause'

Last Friday, a network of fans, mostly ultra groups, published an open letter. It read: "The actual shame lies in the behaviour of the associations, first of all the German FA."

The main aim of the punishments was censorship, it claimed. They said they "won't tolerate what has happened" and will "accept the consequences" as they continue to protest. The tone was confrontational but the points addressed had been made before. Bayern's ultras have for a long time fought against discrimination, homophobia and racism, and they took a stand against the club's sponsorship agreement with Qatar Airways over the nation's human rights record.

They were also the ones who kept alive the memory of the club's Jewish president, who was deported by the Nazis in 1938. After the Hoffenheim game, it was reported by TV broadcasters that Bayern would take all season tickets away from the ultras group for their behaviour. The reports haven't been confirmed yet, and in Sunday's home match against Augsburg, the ultras showed up as usual and presented banners that read: "The ugly face of this club is from people taking blood money from Qatar."

It wasn't the only banner displayed during the previous weekend. In nearly every German stadium, fan groups protested against Hopp, the DFB and Bayern. The Freiburg fans wrote: "Owners protected and wooed. Ordinary people bullied. Football in 2020."

There were no strikes or abandonments. The protests of the supporters were viewed as creative and appropriate in the public eye. The DFB announced plans to work with supporter organisations on the implementation of the three-step plan and stressed its appreciation of creative and critical fan culture. Their words seemed to be an attempt to ease the situation.

But protests will surely continue and the relationship between clubs and fan groups will face more significant tests in the following weeks.

One possible conclusion to draw for now is that there is no alternative to dialogue, as Dortmund sporting director Michael Zorc has said.

But with no real ending in sight, it's nonetheless interesting to note three perhaps unexpected developments in this evolving story.

First, it started off with a crude and distasteful banner depicting a man in crosshairs that, in the end, opened up a public debate on collective punishment and how to tackle discrimination and corruption.

Secondly, after the Hoffenheim-Bayern game, several officials and TV experts demanded fan organisations be thrown out of the stadiums. This week, the stadiums are indeed empty but not because of sanctions or boycotts but because of the coronavirus outbreak. So when the Rheinderby between Cologne and Monchengladbach or the Revierderby between Schalke and Dortmund are played in front of empty seats, the atmosphere will give an impression of what ultra groups keep saying and what legendary Celtic manager Jock Stein once put this way: "Football without fans is nothing."

Thirdly, on Tuesday, the left-wing newspaper Tageszeitung printed a picture of empty stands with the headline: "Coronavirus, you son of a whore!"