Swing bowling
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Swing bowling is a technique used for bowling in the sport of cricket. Practitioners are known as swing bowlers. Swing bowling is generally classed as a subtype of fast bowling.
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[edit] Physics of swing bowling
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 four factors:
- The raised seam of the cricket ball
- Asymmetry in the ball caused by uneven wear of its surface
- The speed of the delivery
- The bowler's action
The asymmetry of the ball is encouraged by the constant polishing of one side of the ball by members of the fielding team, while allowing the opposite side to deteriorate through wear and tear. Over time, this produces a marked difference in the aerodynamic properties of the two sides.
At speeds around 80 mph (around 130 km/h), the airflow around the ball is in transition between smooth, or laminar flow, and turbulent flow. At speeds of 90 mph (around 145 km/h) and above, all the flow is turbulent. A medium-pace bowler, working at 75 to 80 mph (around 120 to 130 km/h), takes advantage of this. In this critical region, the raised seam and other minor imperfections in the ball's surface can induce turbulence while air flowing over other parts of the ball remains laminar. Turbulent air separates from the surface of the ball later than laminar flow air, so that the separation point moves to the back of the ball on the turbulent side. On the laminar flow side it remains towards the front. The result is a net force in the direction of the turbulent side.
Thus by keeping the seam and roughness to one side, the bowler induces the ball to swing in that direction. Skilled bowlers can even make a ball swing one way, and then 'break' the other way upon bouncing, with an off cutter or leg cutter hand action.
The swing of a cricket ball is not caused by the Magnus effect, which gives rise to a force perpendicular to the axis of rotation (in this case up or down). The deviation of a swinging cricket ball is parallel to the axis of its rotation.
[edit] Conventional swing
Typically, a swing bowler aligns the seam and the sides of the ball to reinforce the swing effect. This can be done in two ways:
- Outswinger: 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.
- Inswinger: 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.
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.
It is a common belief amongst both players and fans that balls swing more in humid weather conditions, although no objective research exists to bear this out. These days there is a distinct lack of left-arm swing bowlers in the game. Some of the more famous left-arm bowlers are Pakistan's Wasim Akram and Australia's Alan Davidson.
[edit] Reverse swing
Pioneers and notable practitioners of reverse swing have mostly been Pakistani fast bowlers. Former Pakistan international Sarfraz Nawaz was the founder of reverse swing during the late 1970s, and he passed his knowledge on to former team-mate Imran Khan[1], who in turn taught the duo of Wasim Akram and Waqar Younis. The English pair of Andrew Flintoff and Simon Jones are also well known for the ability to reverse swing the ball. Waqar Younis taught Jones, his then Glamorgan team mate, the skill, who went on to instruct Flintoff.[2]
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, but today they are considered to simply have been ahead of their time.
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 can begin to swing towards the polished side rather than the rough side. This is known as reverse swing (Andrew Flintoff and Simon Jones have been known to produce reverse swing in balls as young as 15 overs old[2]). In essence, both sides have turbulent flow, but here the seam causes the airflow to separate 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. (See External Links.)
Reverse swing is difficult to achieve consistently, as it relies on uneven wear of the ball, tends to occur mostly in hot, dry weather conditions, and requires bowling at high speed. Normal swing can be achieved at relatively moderate bowling speeds, but only the fastest bowlers can regularly produce reverse swing.
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 to 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 reverse as it approaches the batsman, giving its trajectory an S-shape through the air.
Controversy regarding reverse swing has never left modern cricket, as the Pakistani team was accused of ball tampering by the controversial Australian umpire Darrell Hair during the fourth test against England in 2006 when the ball began to reverse swing after the 50th over. His co-umpire Billy Doctrove fully supported him in this action. A hearing subsequently found that there was insufficient evidence to convict anyone of ball tampering.
[edit] See also
[edit] External links
- The Science of Swing. Archived from the original on 2007-02-05.
- Excerpt from DG Bradman's The Art of Cricket describing swing bowling.
- The Basics of Swing bowling explained by M.R.Baig on Cricketfundas.com
- Mysterious art of reverse swing baffles even cricket experts
- Reverse swing or super swing?
- The science of swing bowling
