I’ve often wondered why we use the word derby to refer to a match between two sporting rivals (in most forms of English at least, as the term crosstown rivalry is also used in the United States), considering that Derby is also the name of a city in England. I’d always imagined there must be a connection between the two uses of the word.
And there is, but perhaps not so directly. The exact origin of the use of the word in a sporting sense is unclear, but it’s most-commonly believed to be derived from The Derby: a prestigious horse race in England named after its founder, The 12th Earl of Derby, with the first race run in 1780. It’s quite likely that after the race became popular, the term derby was applied to other major sporting events, particularly matches between great rivals.
Another possible origin though, is in the old ritual of Shrovetide football, an annual English event first played in the town of Derby before medieval times. This was an early precursor to both football and rugby, and was a chaotic and violent affair to say the least, often involving up to 1,000 players, and more than a few fatalities. It’s still a popular annual event in the town of Ashbourne, though a little more civilized nowadays.