Is Fleetwood Town's defeat of Arsenal the biggest upset in League Cup history?

Fleetwood Town pulled off a stunning League Cup upset by defeating Arsenal in a penalty shootout on Tuesday. Arsenal, the reigning Premier League champions, fell behind in the 21st minute to a goal from Aaron Loupalo-Bi, and although Viktor Gyökeres equalised early in the second half, neither side could find a winner in 90 minutes. The result is being debated as potentially the biggest upset in League Cup history, given Arsenal had lost just once in their previous 11 league and Champions League fixtures this season.