Derby day generally refers to any sporting event featuring a pair of sports teams engaged in a local rivalry. (The term originated from association football, for the day when a certain local derby takes place.)
Derby Day specifically may refer to:
Sports
Epsom Derby, at Epsom Downs Racecourse, England (the original and definitive use of the term referring to the classic race founded in 1780 by Lord Derby) Derby Day (UK), an annual rugby match between University of East Anglia and University of Essex Australia-New Zealand sports rivalries aka Trans-Tasman Derby, match days in several sports between Australia and New Zealand India-Pakistan cricket rivalry aka IndoPak Derby, a match day between India and Pakistan Kentucky Derby, a horse race in the United States Kolkata Derby, a football match day between Indian clubs Mohun Bagan and East Bengal in Kolkata New Zealand Derby Victoria Derby, during the Melbourne Spring Racing Carnival, Australia