The essence of moving the ball sideways through the air is known as swing bowling. In favorable conditions, swing bowlers can evoke doubts in the brain of batsmen as which side the cherry will move on.
Several factors contribute to the degree of swing achieved, be it the angle of the seam to the direction of delivery, the condition of the ball, the speed of the delivery or the action of the bowler.
With polishing on either side and tearing of the ball, on the other hand, leads to deterioration of the ball causing a change in the aerodynamic properties of both sides. Due to contrast turbulence, air takes different times to travel around the ball for both halves which contributes to the generation of low pressure and high-pressure regions. Force-induced due to the pressure gradient between two hemispheres accounts for the swing of the ball. This is how the phenomenon of conventional swing occurs.
With the progress of the game, the ball gets older, tearing takes place, and there is an asymmetry in the roughness. A significant reduction in the amount of conventional swing offered is observed showing signs for the factor of reverse swing to come into the play.
The reverse swing takes place using the same concept of that of conventional swing regardless of some existing misconceptions. While polishing the ball, several fluids are used such as saliva, sweat, hair oil, or some gelly material.
Recent years observed use of such illegal practices such as the familiar Sandpaper Saga which led to bans, imposed on three Aussies including their captain and vice-captain. These fluids penetrate through the porous membrane of the leather ball.
Fluids began to expand; their expansion leads to raised bumps over the shiny surface which increases its surface area and is held responsible for air trapping between these bumps. Formation of low-pressure and high-pressure area occurs, and air naturally shifts from high pressure to the low-pressure region. Thus the ball moves towards the shiny side which is just opposite to the case of natural swing.
Reverse swing is observed very late, so it becomes tough for the batsman to play for it. Great bowlers of reverse swing involved Wasim Akram, Waqar Younis from Pakistan and Zaheer Khan from India and James Anderson from England.