Rackets or racquets is an indoor racket sport played in the United Kingdom, United States, and Canada. The sport is infrequently called "hard rackets", to distinguish it from the related sport of squash (also called "squash rackets"). History Historians generally assert that rackets began as an 18th-century pastime in London's King's Bench and Fleet debtors' prisons. The prisoners modified the game of fives (in the process creating Bat Fives) by using tennis rackets to speed up the action. They played against the prison wall, sometimes at a corner to add a sidewall to the game. Rackets then became popular outside the prison, played in alleys behind pubs. It spread to schools, first using school walls, and later with proper four-wall courts being specially constructed for the game. The lithograph at right from the late 1700s shows school boys 'hitting up' outside the Harrow School 'Old School' buildings. Eglinton Castle in Scotland, now largely demolished, had a "Racket Hall" which is first shown on the 1860 OS map, but estate records show that it was built shortly after 1839, the first recorded match being in 1846. The floor is of large granite slabs, now hidden by the wooden floor. It is the very first covered racket court and is now the oldest surviving court in the world, as well as being the oldest indoor sports building in Scotland. It has been restored as a racket hall, but used as an exhibition area. Some private clubs also built courts. Along with real tennis and badminton, rackets was used as an inspiration for the game of lawn tennis, which Walter Clopton Wingfield claimed he invented in 1873, but this was not so, as others had been playing lawn tennis since as early as 1859, including J.B. Perera and Harry Gem. Wingfield did obtain a patent on his proposed peculiarly-shaped "hourglass" lawn tennis court in 1874, but it lasted in use no more than a year before it was shelved by the Marylebone Cricket Club's 1875 official rules mandating the rectangular court in use both before and after Wingfield's hourglass court. A vacant rackets court built into the University of Chicago's Stagg Field served as the location of the first artificial nuclear chain reaction on December 2, 1942. The Stagg Field court is often mistakenly identified as having been a "squash rackets" court. Rackets was part of the 1908 Summer Olympics program and was