FRANKFURT, Germany — There is no match in German football more emotionally charged than the "Ruhr Derby" between Borussia Dortmund and Schalke, neighboring clubs from what used to be the country's heart of coal mining.
The mines are mostly closed and the Ruhr is reinventing itself as a high-tech area, but the rivalry between Dortmund and Schalke remains as deep and hostile as ever.
Clashes between rival fans are frequent and the biggest derby in German football has produced some bizarre moments as well.
Schalke is striving for a place in the Champions League, while Dortmund is seeking to increase the gap to the relegation zone.
While Dortmund hosts Schalke, runaway leader Bayern Munich plays Cologne at home and second-place Wolfsburg has a tough match in Bremen, which undefeated in 2015.
Here are some things to know about the weekend's 23rd round:
One of the weirdest Ruhr Derby incidents occurred in 1969 when Schalke fans invaded the pitch and police used dogs to try to bring the scene under control.
One of the dogs bit Schalke defender Friedel Rausch in the behind. The team doctor gave a Rausch a tetanus shot and he played through the end of the match.
Rausch later became a well-known Bundesliga coach.
One of the most memorable goals in the derby came in 1997, when Schalke's Jens Lehmann became the first goalkeeper to score in the Bundesliga from play and not from the penalty spot.
The goal in injury time secured a 2-2 draw for Schalke.
Lehmann is one of the few players to have played for both Schalke and Dortmund.
With three straight victories, Dortmund appears to have turned around its nightmare season and has jumped from last to 12th, four points from the relegation zone.
Juergen Klopp's team still displays defensive weaknesses and will be missing defender Lukasz Piszczek, who is out for six weeks with a partially torn ankle ligament in the 2-1 Champions League loss at Juventus.
"We will try to dictate play and not only react," Dortmund captain Mats Hummels said. "We must show from the opening minute that we want to win."
Schalke's defense will be weakened by the absence of the injured Joel Matip, the latest addition to a long list of injuries during the season.
Schalke has won only one of its last four Bundesliga games and has had trouble finding the target.
The return of striker Klaas-Jan Huntelaar from suspension and injury should provide a boost to Schalke's attack.
Bremen has won five of its last six. Wolfsburg, eight points behind Bayern, is undefeated in its last 10 and has won the last three.
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