Nottingham Forest players were attacked by a spectator as they celebrated a goal against Leicester City.
The Championship side enjoyed a comfortable 4-1 win against Brendan Rodgers' team, scoring three goals in the space of nine minutes in the first half before Kelechi Iheanacho pulled one back for the visitors.
Forest did not stop there, however, as Djed Spence struck just after the hour mark to restore their three-goal lead and ensure they progress to the next round.
What happened?
As the Forest players gathered in front of the stands to celebrate their third goal of the game, a fan ran on and threw punches at them.
He was immediately pushed away by some players while stewards knocked him to the ground and police escorted him from the field.
What next?
Neither team nor the Football Association have released a statement regarding the incident as of yet.
The fan will likely be arrested and charged by police while a stadium ban could also be handed out.
The 4-1 win sees Nottingham Forest go through to the fifth round of the competition, where they will meet Huddersfield Town.
Leicester are now three games without a win and Rodgers' team are next in action on Thursday, when they face Liverpool at Anfield in the Premier League.