Thursday, December 2, 2010

All about Swing bowling -Mechanism, physics, comparison between conventional and reverse swing,ball tampering



It is a well-known fact that when a bowler maintains perfect swing of the ball, he has every chance of getting batsman into trouble. Some of the greatest swing bowlers of all time are Wasim Akram, Waqar younis,McGrath, and Chaminda Vaas. Here we present you an article on Swing bowling.



Physics behind swing bowling

There are basically four factors that govern swing of the cricket ball: Seam, Asymmetry in ball due to uneven tear, Speed and Bowling Action.



Before proceeding, let's get acquainted with some concepts of fluid mechanics:

As ball is flowing through air, a thin layer of air called "Boundary Layer" is formed along the ball's surface.
This boundary layer does not remain attached to the ball's surface but tends to separate, the phenomenon being called "Boundary Layer Separation".The location of the point where Boundary Layer separates is the factor that decides the pressure distribution around the ball. Pressure Distribution around the ball then decides any lateral force acting on the ball.
The flow of air through the ball can be laminar or turbulent.




Conventional Swing
When given the new ball at the start of an innings, the fast bowlers generally use the raised seam of the ball to create swing. The ball is held with the seam at an angle of around 20 degrees to the direction in which the ball is headed. This creates the following effect as the ball traverses the air; the side with the seam represents a rough surface that causes the air flowing over it to become turbulent, whereas the air flows smoothly over the other side of the ball with the smooth surface. Turbulent air is at a lower pressure than smooth flowing air, causing a pressure difference on the ball, which creates a side force resulting in the ball moving sideways.





So an in-swinger to a right-handed batsman is bowled by holding the ball with the seam pointing slightly to the right causing the ball to move inwards and towards the batsman. An out-swinger to a right-handed batsman is bowled with the seam pointing to the left causing the trajectory of the ball to move outwards before coming back sharply to the batsman. In short, for conventional swing, the ball swings in the same direction as that in which the seam is pointing.
As the innings progresses, the ball goes through wear and tear and every effort is made to polish the ball on one side so it is as smooth as possible while letting the other side deteriorate. This has the same effect as above, causing turbulent air to flow on the rough side and smooth air to flow on the polished side resulting in a sideways drift. For this type of swing, the seam is aligned in the vertical position with the rough side of the ball on one side and the polished side on the other. The direction in which the ball swings is largely determined by the bowling speed.

Reverse Swing

Another type of swing, particularly attributed to bowlers of sub continent, is reverse swing. This generally tends to occur later in the game when the ball is older and has somewhat deteriorated. This effect is usually only significant at very high speeds, however, it can also occur at lower speeds if the ball is considerably roughened. Of course, this type of swing has also garnered significant media attention as numerous players have been accused of deliberately scuffing the ball with foreign objects. The rougher the surface of the ball becomes, the lower the speeds you need to bowl to achieve reverse swing. At high enough bowling speeds and as the ball becomes rougher, it swings in the direction opposite to the alignment of the seam.


Comparison between normal conventional swing and reverse swing
NORMAL CONVENTIONAL swing.
1. Fast-Medium or Medium-Fast
2. Bowled around 70-80mph
3. New ball only
4. Seam position towards 1st/2nd slip
5. 'Rough' side facing slip
6. Ball may move away or inwards from RHB

REVERSE swing:
1. Fast or (a few) Fast-medium bowlers
2. Bowled over 85-90mph
3.Generally bowled using an old ball
4. Seam position towards 1st/2nd slip
5. Shiny side of the ball facing slip
6. Ball moves away from RHB

Ball tampering
There are many rules in cricket regarding the balls. Players can spit and rub the balls to make it smooth, but they cannot apply any lotions or cream to do so. By no means are they allowed to make the ball rough.Recently the term "ball tampering" is gaining coverage in popular media.nder Law 42, subsection 3 of the Laws of Cricket, the ball may be polished without the use of an artificial substance, may be dried with a towel if it is wet, and have mud removed from it under supervision; all other actions which alter the condition of the ball are illegal. These are usually taken to include rubbing the ball on the ground, scuffing with a fingernail or other sharp object, or tampering with the seam of the ball.


The Pakistani cricket team were arguably the first to come under scrutiny, when they were together in 1992 accused of ball-tampering to achieve large amounts of reverse swing. However, no evidence of wrongdoing was ever found in that series. Because of these allegations, in 1996, Imran Khan sued Ian Botham for slander and libel in a British court, and was awarded £400,000.Waqar Younis became the first player to receive a suspension for ball-tampering after a match in 2000.Then England captain Michael Atherton was accused of ball tampering during the a Test match with South Africa at Lord's in 1994 after television cameras caught Atherton reaching into his pocket and then rubbing a substance on the ball. Atherton denied ball tampering, claiming that he had dirt in his pocket which he used to dry his hands. Atherton was summoned to the match referee and was fined £2,000 for failing to disclose the dirt to the match referee.In January 2004, India's Rahul Dravid was fined after he rubbed a half-eaten lolly onto one side of the ball during an ODI. Such instances of using sweetened saliva are not uncommon, as many players claim that the sugary saliva caused by eating confectionery is more effective in polishing the ball than normal saliva. Marcus Trescothick claimed in his autobiography that England's players achieved their prodigious amounts of reverse swing in their successful 2005 Ashes series against Australia by using saliva sweetened by eating mints.

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