The catcalls started before the match even began. When Mats Hummels joined his Dortmund teammates in a shooting exercise during the warm-up before the home game Saturday against Wolfsburg, each of his attempts was accompanied by shrill whistles.
The same happened during the game. Whenever Dortmund's captain touched the ball, the BVB Ultras voiced their disgust. The longer this went on, the more appalled other fans became. They felt it was an unwritten law that you do not boo your own player, even if he has just put in a transfer request.
There were scattered cheers when Hummels played a fine, floating pass on 15 minutes. For the rest of the game, some fans booed his every touch of the ball, but others applauded whatever he did. The majority watched passively and tried to pretend everything was normal.
Of course, it was not. It very rarely is when a player moves from Bayern Munich to Dortmund or vice versa. Considering there have been relatively few such transfers in the past, it's astonishing how many have caused a furor. In fact, the first high-profile deal between the teams instantly triggered trouble.
That was the transfer of Michael Rummenigge, the younger brother of Karl-Heinz. Last week, amid the Hummels brouhaha, his move from Munich to Dortmund in 1988 was widely described as the first between Bayern and Borussia. Even Kicker magazine, the all-knowing bible of the German game, overlooked the true pioneer.
The oversight was easy to make, as even Bayern fans with an encyclopedic knowledge will hardly remember a player called Burkhard Segler wearing their colours. In the summer of 1973, the 22-year-old striker joined Bayern from second-division Osnabruck because there were rumors that Gerd Muller was about to leave for Barcelona.
However, this spectacular transfer eventually came to nothing, and suddenly Segler was facing the prospect of many years on the bench. When Dortmund, then also in the lower flight, came in with a last-minute offer, Segler jumped at the chance. He switched clubs in August, with the season already underway but without having appeared in a game for Bayern. Incidentally, the Dortmund team he joined included a Munich-born player by the name of Helmut Nerlinger, who had started his career at Bayern back in the 1960s.
After the Segler deal, no player moved directly from one club to the other for 15 years. Dortmund didn't have the money to lure even Bavarian benchwarmers to the Ruhr valley, while their players usually lacked the individual class to make them Bayern targets. This gradually changed toward the end of the 1980s. First, Dortmund secured the services of Frankfurt's midfield talent, Andreas Moller. Then they signed Michael Rummenigge from Bayern for around £470,000.
It was a good deal. Dortmund's fans should have been happy, as the transfer signaled that the days of fighting against relegation were over. Instead, they were up in arms. Supporters have good memories, and nobody in Dortmund had forgotten the so-called "locksmith affair," which had almost cost Rummenigge his Bayern job four years earlier.
In April 1984, the player took part in an event in which fans could talk to him on the phone. One of the callers was a locksmith who suggested footballers were overpaid. He compared Rummenigge's wages with his own unemployment benefit, and the player, barely 20 at the time, went through the roof. Rummenigge rudely replied that he deserved his wages, as he delivered "top-level performances," while claiming the locksmith didn't. Rummenigge added that the caller should stay away from football grounds if he didn't accept this.
The conversation was captured on film because a television station was preparing a feature about Rummenigge's fledgling career in the long shadow cast by his famous brother. When the documentary aired six months later, it caused indignation across the country. Rummenigge publicly apologized, but the affair cast him as spoiled and out of touch with reality.
As far as Dortmund's fans were concerned, he was a typically arrogant Bayern player and thoroughly misplaced in the working-class Ruhr valley. Borussia were flooded with protest letters, supporters staged demonstrations in front of the clubhouse, and when Dortmund opened the season with a game against a local amateur club, Rummenigge was booed. To avert a crisis, the club sent him on a goodwill tour. Two years ago, he recalled: "The club's treasurer took me along to every single supporters club, so that people could get to know me as a person. That improved my relationship with the fans. I also got stuck in and changed my playing style."
At the end of his first season, Dortmund won the cup -- the club's first trophy in 23 years. When Rummenigge left Borussia in 1993 to see out his career in Japan, he had become one of the most respected players in the team and was regarded as an honorary Ruhr lad.
The same could not be said of Thomas Helmer, his Dortmund teammate until the previous summer. Helmer had been a key member of a Borussia side that was clearly going places under coach Ottmar Hitzfeld. That's why observers suspected Bayern were trying to hurt a potential rival before he became too big when they began to lure Helmer to Munich toward the end of the 1991-92 season. The player had a get-out clause in his contract that said he could join a foreign club for only £1 million, way below his market value.
That gave Hoeness and Helmer's agent an idea. What if they could find a foreign team willing to sign Helmer and ten immediately pass him on to Bayern? That team was supposed to be French club Auxerre. Today, Helmer says: "At the end of the day, both Bayern and I rejected this plan." But it wasn't as if they had come to their senses -- simple public pressure made them reject the plan.
A DFB committee was asked to look into the legality of the Auxerre ploy. One of its members, Bremen's president Franz Bohmert, told Bild that although the maneuver would not break the letter of the law, "it violates the spirit of the contract between Helmer and Dortmund."
Almost everyone outside Munich felt the same. Bayern eventually signed Helmer fair and square and for what his services were worth. Despite losing Helmer, Dortmund went from strength to strength and were soon in a position from which they could annoy Bayern in the transfer market. In the summer of 2001, the Munich giants approached Freiburg's young midfielder, Sebastian Kehl. The player agreed to join Bayern within the next two years and received a bonus payment for his pledge. Then Dortmund entered the picture and made Kehl an offer. The player returned his bonus (including interest), but Bayern were still miffed.
In December 2001, Hoeness said: "If he doesn't honour the deal we've agreed to, going to labour court might be an option for us." A few weeks later, Kehl joined Dortmund, but Hoeness didn't carry out his threat.
The next big-money transfer between the two clubs produced less bad blood, but there were irritations nonetheless. In 2004, Dortmund missed out on the Champions League, which meant their expensive side could no longer be financed, and they had to sell one or two stars. At the same time, Bayern were bolstering their squad to wrest the league title back from Werder Bremen.
Hoeness took a look at Dortmund's team and said, "Their only player we'd consider is Torsten Frings." According to newspaper reports, this condescending remark "incensed Dortmund's management." In the end, though, Borussia had little choice but to sell Frings and pocket the much-needed £6.2 million.
Despite this cash injection, Dortmund continued to struggle financially. Bayern even gave their rivals a €2 million loan so Borussia could pay their players' wages, including, of course, Kehl's. Still, in 2005 Dortmund almost went bankrupt and were forced to regroup and rebuild.
They did so a lot more quickly than anyone could have imagined. Six years later, in December 2011, Bayern were highly interested in the services of Gladbach's forward, Marco Reus. At the time, Bayern's business manager was Christian Nerlinger, the son of Helmut Nerlinger and a former Dortmund player himself. He said, "When Bayern want to sign a player, they will sign him."
Nerlinger was quoting Hoeness, who had made the same statement 12 years earlier, but he had to eat his words less than two weeks later, when Dortmund announced they had signed Reus for the new season. There is a theory that says it was this embarrassing defeat in the transfer market that led Bayern to come in for Dortmund's rising star, Mario Gotze. The fact that news of Gotze's move to Munich broke on the day before Dortmund met Real Madrid in the 2013 Champions League semifinals only added fuel to the fire.
Barely two months later, Robert Lewandowski announced that he too wanted to join Bayern as soon as possible. Now Dortmund put their foot down and told the player to see out his contract. In so doing, Borussia forewent around €20 million, but nine years after the Frings transfer, the situation had changed. Dortmund needed the player more than they needed the money.
They probably also needed to demonstrate that they couldn't be bossed around. As Borussia's chairman, Hans-Joachim Watzke, later said, Gotze and Lewandowski were not the only Dortmund players Bayern approached in an effort "to destroy the 2012 championship team".
Looking at this long history of accusations and retorts, you have to say that in the past 30 years, there have been only three transfers between the two clubs that did not cause some sort of controversy. The first was Dortmund's signing of striker Jurgen Wegmann in 1989. The second was Dortmund's signing of Christian Nerlinger in 1998.
The third? Dortmund's signing of Hummels in 2008. Oh, the irony.
Uli covers German football and has written over 400 columns since 2002. The author of six books, he is working on an English-language history of Bayern.