The Philadelphia Flyers were playing against their division rivals, the New Jersey Devils. While the Flyers are still fighting for a playoff spot, the Devils have absolutely nothing to lose, as they are already eliminated from postseason play.
The biggest rivalry didn't occur on the ice among the players, but in the stands when a huge fight erupted between two to four fans. This fight coincided with the broadcast of UFC 300, which probably motivated the Devils fans to clash with the Flyers fans.