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.[71]
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.[74] The Laws of Cricket were updated in 2017 to allow substitutes to act as wicket-keepers,[75] a situation that first occurred when Mumbai Indians' wicket-keeper Ishan Kishan was injured in a match on 18 April 2018.[76]
Cricket entered a new era in 1963 when English counties introduced the limited overs variant.[52] As it was sure to produce a result, limited overs cricket was lucrative and the number of matches increased.[53] The first Limited Overs International was played in 1971 and the governing International Cricket Council (ICC), seeing its potential, staged the first limited overs Cricket World Cup in 1975.[54] In the 21st century, a new limited overs form, Twenty20, made an immediate impact.[citation needed] On 22 June 2017, Afghanistan and Ireland became the 11th and 12th ICC full members, enabling them to play Test cricket.[55][56]
Single wicket was popular in the 18th and 19th centuries and its matches were generally considered top-class. In this form, although each team may have from one to six players, there is only one batsman in at a time and he must face every delivery bowled while his innings lasts. Single wicket has rarely been played since limited overs cricket began. Matches tended to have two innings per team like a full first-class one and they could end in a draw.[122]
Captive crickets are omnivorous; when deprived of their natural diet, they accept a wide range of organic foodstuffs. Some species are completely herbivorous, feeding on flowers, fruit, and leaves, with ground-based species consuming seedlings, grasses, pieces of leaf, and the shoots of young plants. Others are more predatory and include in their diet invertebrate eggs, larvae, pupae, moulting insects, scale insects, and aphids.[14] Many are scavengers and consume various organic remains, decaying plants, seedlings, and fungi.[15] In captivity, many species have been successfully reared on a diet of ground, commercial dry dog food, supplemented with lettuce and aphids.[14]