Cricket balls are made from a core of cork, which is layered with tightly wound string, and covered by a leather case with a slightly raised sewn seam. The covering is constructed of four pieces of leather shaped similar to the peel of a quartered orange, but one hemisphere is rotated by 90 degrees with respect to the other. The "equator" of the ball is stitched with string to form the seam, with a total of six rows of stitches. The remaining two joins between the leather pieces are left unstitched.
For men's cricket, the ball must weigh between 5.5 and 5.75 ounces (155.9 and 163.0 g) and measure between 8 13/16 and 9 in (224 and 229 mm) in circumference. Balls used in women's and youth matches are slightly smaller.
Cricket balls are traditionally dyed red, and red balls are used in Test cricket and First-class cricket. White balls were introduced when one-day matches began being played at night under floodlights, as they are more visible at night. Professional one-day matches are now played with white balls, even when they are not played at night. Other colours have occasionally been experimented with, such as yellow and orange for improved night visibility, but the colouring process has so far rendered such balls unsuitable for professional play because they wear differently to standard balls. Recently the ICC is in talks for testing with pink balls in ODI matches. The white ball has been found to swing a lot more during the first half of the innings than the red ball. It also deteriorates faster than the red ball.
Cricket balls are expensive. As of 2007, the ball used in first class cricket in England has a recommended retail price of £70 (USD 140). In test match cricket this ball is used for a minimum of 80 overs (theoretically five hours and twenty minutes of play). In professional one day cricket, at least two new balls are used for each match. Amateur cricketers often have to use old balls, or cheap substitutes, in which case the changes in the condition of the ball experienced during an innings in professional cricket are not replicated.
The ball is not replaced if it is hit into the crowd - the crowd must return it. If the ball is damaged, lost, or illegally modified, it will be replaced by a used ball in similar condition to the replaced ball. A new ball can only be used after the specified minimum number of overs have been bowled with the old one.
Because a single ball is used for an extended period of play, its surface wears down and becomes rough. The bowlers will polish it whenever they can - usually by rubbing it on their trousers, producing the characteristic red stain that can often be seen there. However, they will usually only polish one side of the ball, in order to create 'swing' as it travels through the air. They may apply natural substances (i.e. saliva or sweat) to the ball as they polish it.
The seam of a cricket ball can also be used to produce different trajectories through the air, with the technique known as swing bowling, or to produce sideways movement as it bounces off the pitch, with the technique known as seam bowling.
Since the condition of the cricket ball is crucial to the amount of movement through the air a bowler can produce, the laws governing what players may and may not do to the ball are specific and rigorously enforced. The umpires will inspect the ball frequently during a match. It is illegal for a player to:
Despite these rules, it can be tempting for players to gain an advantage by breaking them. There have been a handful of incidents of so-called ball tampering at the highest levels of cricket, involving players such as Pakistani fast bowler Waqar Younis and former England captain Mike Atherton.
A new cricket ball is harder than a worn one, and is preferred by fast bowlers because of the speed and bounce of the ball as it bounces off the pitch. Older balls tend to spin more as the roughness grips the pitch more when the ball bounces, so spin bowlers prefer to use a worn ball. Uneven wear on older balls may also make reverse swing possible. A captain may delay the request for a new ball if he prefers to have his spin bowlers operating, but usually asks for the new ball soon after it becomes available.
Cricket balls are notoriously hard and potentially lethal, hence today's batsmen and close fielders often wear protective headgear. Raman Lamba was killed when hit on the head while fielding at forward short leg in a club match in Bangladesh. Only two other cricketers are known to have died as a result of on-field injuries in a first-class fixture. Both were hit while batting: George Summers of Nottinghamshire on the head at Lord's in 1870; and Abdul Aziz, the Karachi wicket-keeper, over the heart in the 1958-59 Quaid-e-Azam final. The last cricketer to die after being hit in any match was Ian Folley of Lancashire, playing for Whitehaven in 1993.
Frederick, Prince of Wales is often said to have died of complications after being hit by a cricket ball, although in reality this is not true - although he was hit in the head by one, the real cause of his death was a burst abscess in a lung. Glamorgan player Roger Davis was almost killed by a ball in 1971 when he was hit on the head while fielding.
Normal swing is achieved by keeping one side of the ball polished smooth and shiny, and delivering the ball with the polished side forward, and the seam angled in the direction of desired swing. The outswinging delivery moves away from the right-handed batsman, while the inswinger moves in towards him. Normal swing is achieved by maintaining laminar boundary layer air-flow on the shiny side whilst creating turbulent flow on the seam side. These deliveries, particularly the outswinger, are the bread and butter of opening bowlers who get to use the ball while it is still new.
Reverse swing is very different from conventional swing. Although the seam is oriented in the same way as for an outswinger and the action is the same, the rough side of the ball is to the fore, and the ball moves in to the batsman like an inswinger. Reverse swing is achieved when the ball is bowled very fast. In this case the air flow will become turbulent on both sides before it reaches the seam.
Many casual players use a tennis ball wrapped in layers of some type of adhesive tape (often electrical insulating tape), which makes the relatively soft tennis ball harder and smoother. This is commonly referred to as a taped ball. A common variant is to tape only half the tennis ball, to provide two different sides and make it easy to bowl with prodigious amounts of silky swing.