Borussia Dortmund boss Lucien Favre criticised the referee's decisions as his nine-man side slumped to a 4-2 defeat to Schalke, putting a significant dent in their title hopes.
In an action-packed Revierderby, Dortmund led through Mario Gotze before Schalke were awarded a penalty for handball from which Daniel Caligiuri equalised.
Salif Sane put them ahead before Marco Reus and Marius Wolf were both shown red cards in a five-minute spell spanning Caligiuri's second goal. Axel Witsel pulled one back but Breel Embolo made the game safe.
"That's extremely hard to take, above all given the way we played," Favre told bvb.de.
"We started really well, showed a lot of patience and scored a fantastic goal. Then five minutes later, it's up to the referee to have a look at a handball.
"Anyone who applies the handball rule like that doesn't understand football. It's an absolute disgrace."
On the decision to send him off, Reus added: "We do not need to talk about whether it was a red card. I didn't want to do my opponent any harm, I just arrived a bit late and ended up catching him."
Defeat means second-placed Dortmund could find themselves four points behind Bayern Munich by the end of the weekend, should the leaders win their game in hand against Nurnberg on Sunday, but administrator Sebastian Kehl insisted the club were not going to give up with three games left.
"Playing with nine men in the later stages of the game was tough," he said. "We lost the derby – that's hard to accept.
"Obviously we had to try and win all of our matches in order to have a shot at realising our dream, but I'm not giving up just yet."
Huub Stevens was happy with his Schalke side's performance as they took a significant step to guaranteeing safety, moving nine points ahead of Stuttgart in the relegation play-off place.
Stevens said in quotes published on the club's Twitter feed: "Of course we are very happy about the derby victory.
"A big compliment to the team. The boys were very tight in training during the week and did an excellent job of implementing the tactics.
"If you win 4-2 here in Dortmund, then you can be very happy about that."