The essence of swing bowling is to get the cricket ball to deviate sideways as it moves through the air towards or away from the batsman. In order to do this, the bowler makes use of five factors:
The raised seam of the cricket ball
The wear and tear on the ball
The polishing liquid used on the ball
The speed of the delivery
The bowler's action
An outswinger to a right-handed batsman can be bowled by aligning the seam slightly to the left towards the slips and placing the roughened side of the ball on the left. To extract consistent swing, a bowler can also rotate his wrist toward the slips while keeping his arm straight. To a right-handed batsman, this results in the ball moving away to the off side while in flight, usually outwards from his body.
An inswinger to a right-handed batsman can be bowled by aligning the seam slightly to the right and placing the roughened side of the ball on the right and towards leg slip. To extract consistent swing, a bowler can also rotate or "open up" his wrist towards leg slip. To a right-handed batsman, this results in the ball moving in to the leg side while in flight, usually inwards towards his body. Also, Waqar Younis employed the technique of covering the ball with his hands during his run up to hide the grip.
The curvature of swing deliveries can make them difficult for a batsman to hit with his bat. Typically, bowlers more commonly bowl outswingers, as they tend to move away from the batsman, meaning he has to "chase" the ball in order to hit it. Hitting away from the batsman's body is dangerous, as it leaves a gap between the bat and body through which the ball may travel to hit the wicket. Also, if the batsman misjudges the amount of swing, he can hit the ball with an edge of the bat. An inside edge can ricochet on to the wicket, resulting in him being out bowled, while an outside edge can fly to the wicket-keeper or slip fielders for a catch.
An inswinger presents relatively fewer dangers to the batsman, but can result in bowled or leg before wicket dismissals if the batsman misjudges the swing on the ball.
An inswinger combined with a yorker can be especially difficult for the batsman to defend against, especially if used as a surprise delivery after a sequence of outswingers.
There has been a distinct lack of left-arm swing bowlers in the game. Some of the most famous left-arm bowlers were Pakistan's Wasim Akram, India's Zaheer Khan, Australia's Alan Davidson and Sri Lanka's Chaminda Vaas.
Normal swing occurs mostly when the ball is fairly new. As it wears more, the aerodynamics of the asymmetry change and it is more difficult to extract a large amount of swing. When the ball becomes very old—around 40 or more overs old—it begins to swing towards the shine. This is known as reverse swing—meaning a natural outswinger will become an inswinger and vice versa. In essence, both sides have turbulent flow, but here the seam causes the airflow to separate[clarification needed] earlier on one side. The result is always a swing to the side with the later separation, so the swing is away from the seam.
Reverse swing tends to be stronger than normal swing, and to occur late in the ball's trajectory. This gives it a very different character from normal swing, and because batsmen experience it less often, they generally find it much more difficult to defend against. It is also possible for a ball to swing normally in its early flight, and then to alter its swing as it approaches the batsman. This can be done in two ways  one for the ball to reverse its direction of swing, giving it an 'S' trajectory: the other is for it to adopt a more pronounced swing in the same direction in which the swing is already curving; either alteration can be devastating for the batsman. In the first instance, he is already committed to playing the swing one way, which will be the wrong way to address swing which is suddenly coming from the opposite direction: in the second instance, his stance will be one which is appropriate for the degree, or extent, of the expected swing, and which could suddenly leave him vulnerable to LBW, being caught behind, or bowled. Two back-to-back deliveries from Wasim Akram, one of each type, were considered to be the turning point of the 1992 World Cup Final.
Pioneers and notable practitioners of reverse swing have mostly been Pakistani fast bowlers. In the early days of reverse swing, Pakistani bowlers were suspected of ball tampering to achieve the conditions of the ball that allow reverse swing, although the accusations were baseless. Former Pakistan international Sarfraz Nawaz and Sikander Bakht were the founders of reverse swing during the late 1970s, and they passed the knowledge on to former team-mate Imran Khan, who in turn taught the duo of Wasim Akram and Waqar Younis. The English pair of Andrew Flintoff and Simon Jones, having been taught by Troy Cooley and the Indian bowlers like Zaheer Khan, Ajit Agarkar are also well known for the ability to reverse swing the ball..