1 Answer

The phrase most likely originated from The Derby, a horse race in England, founded by the 12th Earl of Derby in 1780, since at least as early as 1840 'derby' has been used as a noun in English to denote any kind of sporting contest. A local derby is just a sporting contest between local rivals. It may be that the Earl, or his ancestors, are responsible for lending their titled name to sporting events, giving rise to the 'derby' match.
Another widely reported theory, though not accepted by the Oxford English Dictionary, is that the phrase came about from the city of Derby itself. The traditional Shrovetide football match was also commonplace in the city. It was renowned as a chaotic and exuberant game that involved the whole town and often resulted in fatalities. The goals were at Nuns Mill in the north and the Gallows Balk in the south of the town, and much of the action took place in the Derwent river or Markeaton brook. Nominally the players came from All Saints' and St Peter's parishes, but in practice the game was a free-for-all with as many as 1,000 players. A Frenchman who observed the match in 1829 wrote in horror, 'if Englishmen call this play, it would be impossible to say what they call fighting'. Though this has been refuted by the Oxford dictionary and hailed as "nothing apart from local folklore ... after all, the phrase isn't 'a local Ashbourne'."
Yet another theory is that the 'derby match' saying arose from when Liverpool played Everton. Their two grounds were separated by Stanley Park, owned by the Earl of Derby. This latter suggestion can be discounted, however. The Widnes Weekly News of 9 March 1889 describes a game between the (rugby) football team of that town and the touring M?ori as 'the local Derby'. This usage was three years before Liverpool FC came into existence.
Another theory is that the term applies not to the match itself but to the size of the crowd. In the early years of the twentieth century, the largest sporting crowd in England was at the annual Derby horserace meeting where more than half a million people would pack Epsom Downs to watch the race. At that time football matches were attended entirely by 'home' supporters – the concept of the 'away supporter' lay many years into the future as the largely working-class crowds could not afford to follow their teams around the country. Supporters watched the first team and reserves who were 'at home' on alternate Saturdays. The only exception came when two teams from the same town played one another. Then the 'home' supporters of both teams would turn up, producing the largest gate of the season. The term 'local derby' was coined by the press as an analogy to the Derby race crowd. In time the expression came to refer to the match rather than the size of the crowd.