The ball is a hard leather-seamed spheroid, with a circumference of 22.9 centimetres (9.0 in). The ball has a "seam": six rows of stitches attaching the leather shell of the ball to the string and cork interior. The seam on a new ball is prominent and helps the bowler propel it in a less predictable manner. During matches, the quality of the ball deteriorates to a point where it is no longer usable; during the course of this deterioration, its behaviour in flight will change and can influence the outcome of the match. Players will, therefore, attempt to modify the ball's behaviour by modifying its physical properties. Polishing the ball and wetting it with sweat or saliva is legal, even when the polishing is deliberately done on one side only to increase the ball's swing through the air, but the acts of rubbing other substances into the ball, scratching the surface or picking at the seam are illegal ball tampering.
The inter-war years were dominated by Australia's Don Bradman, statistically the greatest Test batsman of all time. Test cricket continued to expand during the 20th century with the addition of the West Indies (1928), New Zealand (1930) and India (1932) before the Second World War and then Pakistan (1952), Sri Lanka (1982), Zimbabwe (1992), Bangladesh (2000), Ireland and Afghanistan (both 2018) in the post-war period. South Africa was banned from international cricket from 1970 to 1992 as part of the apartheid boycott.
It is generally believed that cricket originated as a children's game in the south-eastern counties of England, sometime during the medieval period. Although there are claims for prior dates, the earliest definite reference to cricket being played comes from evidence given at a court case in Guildford on Monday, 17 January 1597 (Julian calendar; equating to 30 January 1598 in the Gregorian calendar). The case concerned ownership of a certain plot of land and the court heard the testimony of a 59-year-old coroner, John Derrick, who gave witness that:
A phylogenetic study by Jost & Shaw in 2006 using sequences from 18S, 28S, and 16S rRNA supported the monophyly of Ensifera. Most ensiferan families were also found to be monophyletic, and the superfamily Gryllacridoidea was found to include Stenopelmatidae, Anostostomatidae, Gryllacrididae and Lezina. Schizodactylidae and Grylloidea were shown to be sister taxa, and Rhaphidophoridae and Tettigoniidae were found to be more closely related to Grylloidea than had previously been thought. The authors stated that "a high degree of conflict exists between the molecular and morphological data, possibly indicating that much homoplasy is present in Ensifera, particularly in acoustic structures." They considered that tegmen stridulation and tibial tympanae are ancestral to Ensifera and have been lost on multiple occasions, especially within the Gryllidae.
Crickets chirp at different rates depending on their species and the temperature of their environment. Most species chirp at higher rates the higher the temperature is (about 62 chirps a minute at 13 °C (55 °F) in one common species; each species has its own rate). The relationship between temperature and the rate of chirping is known as Dolbear's law. According to this law, counting the number of chirps produced in 14 seconds by the snowy tree cricket, common in the United States, and adding 40 will approximate the temperature in degrees Fahrenheit.
Most male crickets make a loud chirping sound by stridulation (scraping two specially textured limbs together). The stridulatory organ is located on the tegmen, or fore wing, which is leathery in texture. A large vein runs along the centre of each tegmen, with comb-like serrations on its edge forming a file-like structure, and at the rear edge of the tegmen is a scraper. The tegmina are held at an angle to the body and rhythmically raised and lowered which causes the scraper on one wing to rasp on the file on the other. The central part of the tegmen contains the "harp", an area of thick, sclerotinized membrane which resonates and amplifies the volume of sound, as does the pocket of air between the tegmina and the body wall. Most female crickets lack the necessary adaptations to stridulate, so make no sound.
The wicket-keeper and the batsmen wear protective gear because of the hardness of the ball, which can be delivered at speeds of more than 145 kilometres per hour (90 mph) and presents a major health and safety concern. Protective clothing includes pads (designed to protect the knees and shins), batting gloves or wicket-keeper's gloves for the hands, a safety helmet for the head and a box for male players inside the trousers (to protect the crotch area). Some batsmen wear additional padding inside their shirts and trousers such as thigh pads, arm pads, rib protectors and shoulder pads. The only fielders allowed to wear protective gear are those in positions very close to the batsman (i.e., if they are alongside or in front of him), but they cannot wear gloves or external leg guards.
The innings (ending with 's' in both singular and plural form) is the term used for each phase of play during a match. Depending on the type of match being played, each team has either one or two innings. Sometimes all eleven members of the batting side take a turn to bat but, for various reasons, an innings can end before they have all done so. The innings terminates if the batting team is "all out", a term defined by the Laws: "at the fall of a wicket or the retirement of a batsman, further balls remain to be bowled but no further batsman is available to come in". In this situation, one of the batsmen has not been dismissed and is termed not out; this is because he has no partners left and there must always be two active batsmen while the innings is in progress.
If a fielder is injured or becomes ill during a match, a substitute is allowed to field instead of him, but the substitute cannot bowl or act as a captain. The substitute leaves the field when the injured player is fit to return. The Laws of Cricket were updated in 2017 to allow substitutes to act as wicket-keepers, a situation that first occurred when Mumbai Indians' wicket-keeper Ishan Kishan was injured in a match on 18 April 2018.
Crickets have from time to time appeared in poetry. William Wordsworth's 1805 poem The Cottager to Her Infant includes the couplet "The kitten sleeps upon the hearth, The crickets long have ceased their mirth". John Keats's 1819 poem Ode to Autumn includes the lines "Hedge-crickets sing; and now with treble soft / The redbreast whistles from a garden-croft". The Chinese Tang dynasty poet Du Fu (712–770) wrote a poem that in the translation by J. P. Seaton begins "House cricket ... Trifling thing. And yet how his mournful song moves us. Out in the grass his cry was a tremble, But now, he trills beneath our bed, to share his sorrow."