Reverse swing in cricket: A misunderstood art

In cricket, swing is a potent weapon in the battle of willow and leather. There are three basic types of swing: in-swing, out-swing and reverse swing. Reverse swing, whether it goes away from the batsman or otherwise, goes contrary to a batsman’s expectation. The cricket ball swings in a manner contrary to what the seam position and shine of the ball suggests it should.

Based on that, reverse swings is characterized as follows:

• The ball swinging towards the shiny side of the ball as opposed to moving towards the rough side (as in conventional swing)
• The ball moving in the opposite direction of the seam

With conventional swing, the increased drag on the rough side of the ball causes the shinier side to move faster through the air. This creates a side force that acts in the direction of the shiny side. Even with a new ball, an upright, angled seam can generate swing when bowled at high speeds. This seems strange to many, but it depends on the following elements:

• Bowler's bowling action and pace
• The condition of the ball
• Atmospheric conditions – like humidity
• Pitch conditions – a drier pitch roughens both sides of the ball, which is necessary for reverse swing

Scientist Rabindra Mehta, a long-time friend of former Pakistan captain Imran Khan, posited that true reverse swing occurs when the ball moves in a direction opposite to that of the seam position. Seam bowlers, who are not genuinely fast, can generate conventional swing easily. However, this can only occur up to a certain speed threshold, because the higher velocity in the forward motion reduces the impact of the side force necessary for swing. Therefore, for genuinely fast bowlers, the seam position becomes more important in generating swing.

Mehta suggests that the seam position is more prominent because it causes the boundary layer of air around the ball to separate earlier at the top of the ball than at the bottom of it. This argument suggests that bowlers who bowl upwards of 90 miles (140 kilometres) per hour can only generate reverse swing. So what really obtains is that the effect of the turbulent air around the seam outweighs the effect of the pressure differentials of the ball.

Reverse swing bowler Waqar Younis also suggested that a dry pitch was helpful in producing reverse swing. The former Pakistan captain and coach stated that the dry pitch made both sides of the ball rough, although one side was significantly rougher than the other. Waqar also noted that the Pakistan bowlers did not touch the sides of the ball, since this might dampen the ball and reduce the effect. Waqar may have had a point, since reduced side force could have accentuated the importance of the seam position.

Reverse swing was one viewed like a magician’s trick or diabolical effect brought about by ball tampering. The idea that the ball is going the “wrong” way is common, since cricket has terms for balls that goes the “wrong way.” The “googly” and “doosra” are terms used when leg-spinners and off-spinners spin the ball in the opposite direction to what their bowling action suggests.

Looking at the mechanics of the googly or doosra, one would observe what causes the ball to spin the other way. Technically, reverse swing is merely in-swing or out-swing that defies expectation. The idea that the ball “reverses” is just another one of cricket’s “wrong one” analogies. Science shows that there are merely different ways of producing outswing and in-swing. When it’s caused strictly by pressure differentials, it is conventional swing. However, when the swing is caused primarily by the seam, it is reverse swing – just a case of one force over-ruling another.

The reason it took so long for reverse swing to be accepted is its association with ball tampering. This is especially as exponents of reverse swing usually hail from the sub-continent – Pakistan in particular. Indeed, the art and science of reverse swing is not yet fully understood and is barely understood in some quarters of the cricket world. There is merit to the idea that ball tampering can aid reverse swing, however. For example, if the seam position is elevated on the shinier side of the ball, that would create additional turbulence on the shinier side of the ball. This causes the ball to swing in the direction of the shinier side.

One can suppose that reverse swing is to fast bowlers what googlies and doosras are to leg-spinners and off-spinners. It will remain part of cricket’s terminology and certainly will be an additional weapon for fast bowlers on even the most unforgiving pitches.