BERLIN (AP) -- Dealing with a surge of right-wing extremism among its fans, Borussia Dortmund has long used social workers at games to defuse tense situations and help promote tolerance.
This month, however, the social workers themselves ended up being attacked by a group of neo-Nazi fans, with one of them beaten badly in a stadium toilet.
It was one of many recent incidents that highlight how Germany -- and Dortmund in particular -- is still dealing with grim reminders of its dark days of racism, intolerance and violence.
Far-right extremists in the west German city of 600,000 inhabitants have been able to infiltrate some of Borussia Dortmund's fanatical supporter groups, recruiting sympathizers and leading to an upsurge in thuggish behavior and violent attacks.
Dortmund, in the heartland of the industrial Ruhr area, has long been a magnet for immigrants from all over the world. It also serves as a focal point for neo-Nazis in the state of North Rhine-Westphalia. In no other German state are more right-wing offences recorded.
Media reports suggest around 100 neo-Nazis regularly attend games among 24,500 fans on the south terrace, Europe's largest standing-only section, in Dortmund's Westfalen Stadium.
"We believe there are a few right-wing extremists," the club said in a statement. "The authorities say they have not noticed a significant increase in their numbers in recent years. However, there have been significant changes in the type of incidents."
It may be a fringe group, but violence has increased dramatically.
Before Dortmund's Champions League at Shakhtar Donetsk on Feb. 13, fan representative Jens Volke was accosted and struck in the face when he approached three neo-Nazis who were chanting far-right slogans. Ukrainian wardens prevented anything worse happening.
Two of the men then followed Dortmund Fan Project leader Thilo Danielsmeyer to the toilet. The door burst open, and as Danielsmeyer turned around, he was struck in the face. An accomplice kept watch while the beating continued. The assailant kept punching him, kicking him in the back, before trying repeatedly to bash his head against the wall.
The three hooligans have been identified by the club and banned from stadiums across Germany. They each face charges of causing grievous bodily harm and verbal abuse.
"The actions were despicable and represent an absolute taboo," Dortmund managing director Hans-Joachim Watzke said.
The club has pledged "zero tolerance" for right-wing extremism but faces an escalating struggle as neo-Nazis answer with displays of defiance and violent acts of reprisal.
Danielsmeyer was a logical target. The Dortmund Fan Project was founded in 1988 to combat xenophobia and racism, while promoting a message of tolerance and inclusion to troubled young men.
Lately however, members have drifted away from the group and become more receptive to far-right ideology - and to violence.
Rioting at the Ruhr derby between Dortmund and Schalke last October was the worst seen in the area for years. In all, 180 arrests were made and 11 people were injured, including eight officers.
Fans had the "potential for violence not seen for a long time," Dortmund police spokesman Michael Stein said.
And they're being urged on by an older generation of violent fans who were at the center of the rise of hooliganism in the 1980s.
"I'm so proud of my boys!" Siegfried Borchardt told 11Freunde magazine after the October riots. "Didn't they really give it gas, my boys, eh?"
Better known as SS-Siggi, Borchardt helped form the infamous Borussenfront group of hooligans in 1982. It became notorious for brawling after matches and targeting Turks in Dortmund's north inner city.
The 59-year-old Borchardt has served prison terms for assault, incitement to hatred and disturbing the peace, but is no longer involved first-hand in any violent activities as a new generation of neo-Nazis has taken over.
While Borussenfront members are banned from attending Bundesliga games, they continue to meet at lower division games, and have had success spreading their right-wing ideology among other fan groups. Beer, football and a common enemy in rival fans or the police help lay the foundations.
Members of the Desperados group of ultras and others such as the Northside group have swayed right in recent years, and now meet with members of the Borussenfront to train for street battles.
"There has long been the second and third generation," Borchardt said.
While membership of neo-Nazi groups has dropped in Germany, the number of far-right extremists prepared to use violence has grown, the country's domestic intelligence agency found last year.
Dortmund's neo-Nazis have become more prominent since German interior minister Ralf Jaeger banned the violent far-right National Dortmund Resistance (NWDO) group last August. Members of the NWDO often overlap with those of the Desperados, Borussenfront or Northside ultras and they have taken their protest to the stands.
A banner proclaiming "Solidarity with the NWDO" was displayed prominently during the club's opening game of the Bundesliga on Aug 24. A 27-year-old known neo-Nazi was identified and banned from all German stadiums.
Six days previously, a banner extending sympathy to a deceased member of the "Hoonara Chemnitz" group was displayed in the Dortmund fan block at a German Cup game. "Hoonara" is an abbreviation of the words Hooligans, Nazis and Racists.
Eight neo-Nazis were banned from attending games across Germany for unfurling right-wing symbols and banners - including an imperial war flag - during a game played by Dortmund's second team at Rot-Weiss-Erfurt on Sept. 1. The Frankfurter Allgemeine Zeitung newspaper said most of them were members of NWDO.
One Desperado, known as a member of the NWDO, was imprisoned in September for his part in a masked-attack on left-wing youths, who were hounded out of their bus, pelted with stones and bottles and threatened with a knife.
Dortmund employs nearly 800 wardens to cover a stadium with a Bundesliga capacity of 80,720. The club has also invested €250,000 in a camera system to help monitor fan behavior during games. All banners or symbols with far-right associations have been banned. Fan projects are promoted and the club works closely with police and the Bundesliga authorities.
It might find out soon whether any of the measures are working -- the next Ruhr derby, at Schalke, is coming up on March 9.