Reverse swing
| Types | |
|---|---|
| Fast |
|
| Spin | |
| Deliveries | |
| Fast | |
| Spin | |
| Other | |
| Actions | |
| Usual | Overarm |
| Other | |
| Illegal techniques | |
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.
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. To do this, the bowler makes use of five factors:
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. With time, this produces a marked difference in the aerodynamic properties of the two sides.
Both turbulent and laminar airflow contribute to swing. Air in laminar flow separates from the surface of the ball earlier than air in turbulent flow, so that the separation point moves toward the front of the ball on the laminar side. On the turbulent flow side it remains towards the back, inducing a greater lift force on the turbulent airflow side of the ball. The calculated net lift force is not enough to account for the amount of swing observed. Additional force is provided by the pressure-gradient force.
To induce the pressure-gradient force the bowler must create regions of high and low static pressure on opposing sides of the ball. The ball is then "sucked" from the region of high static pressure towards the region of low static pressure. The Magnus effect uses the same force but by manipulating spin across the direction of motion. A layer of fluid, in this case air, will have a greater velocity when moving over another layer of fluid than it would have had if it had been moving over a solid, in this case the surface of the ball. The greater the velocity of the fluid, the lower its static pressure.
When the ball is new the seam is used to create a layer of turbulent air on one side of the ball, by angling it to one side and spinning the ball along the seam. This changes the separation points of the air with the ball; this turbulent air creates a greater coverage of air, providing lift. The next layer of air will have a greater velocity over the side with the turbulent air due to the greater air coverage and as there is a difference in air velocity, the static pressure of both sides of the ball are different and the ball is both 'lifted' and 'sucked' towards the turbulent airflow side of the ball.
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