Reverse Swing

Conventional swing

The cricket ball often moves in the air towards or away from a batsman when a pace bowler is bowling. It is this deviation most fast bowlers strive for because of the problems it causes to the batsmen. Swing is all about aerodynamics. Batsmen are used to facing orthodox swing - which happens when the ball is still relatively hard and new in the first 10 to 15 overs.

However, over the past 20 years fast bowlers have developed a new method of making the ball move in the air with the older ball called 'reverse swing'.

But to obtain any sort of movement, there are a number of factors to consider.

The ball

Fielders are often seen continually shining one side of a ball by rubbing it on their trousers. The rubbing helps to maintain a smooth, shiny side while the opposite is left to deteriorate through normal wear and tear. In simple terms, the aerodynamics of bowling means the air travels faster around the shiny side lowering the air pressure on the shiny side by the Bernoulli Principle causing the ball to deviate in that direction. Other factors also play a part.

Reverse swing

Once the ball becomes older and more worn, it will begin to move in the opposite direction to where it would usually swing with no great change in the bowling grip.

For example, an outswinger's grip will move away from the batsman in the air while an inswinger will move towards the bat. All this tends to happen very late on in the delivery, making it difficult for the batsman to judge the changes in the air. Not every single bowler can obtain reverse swing - the ball needs to be propelled above 80 mph or thereabouts to make it move in the air.

Origin

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 and captain Imran Khan. It was Imran who schooled bowlers Wasim Akram and Waqar Younis, who brought the art to the cricket world's attention during the late 1980s and 1990s. The dynamic duo managed to make the old ball swing a considerable distance at pace in both directions, a skill few bowlers can master.

In a display of reverse swing in a Test match against Australia in 1979 in Melbourne, Sarfraz Nawaz took nine wickets in an innings. This included a remarkable spell of 33 deliveries in which he captured 7 wickets for 1 run. This is when the cricket world noticed this new form of fast bowling.

Wasim Akram then brought reverse swing to the public limelight but the man who really put the reverse into swing was Waqar Younis. He bucked the 1980s trend of pitching fast and short by pitching fast and full. Not an obvious recipe for success until the prodigious late inswing is factored in, which was designed to smash into the base of leg stump or the batsman's toes.

How does it work?

There have been plenty of theories about why, but here's an explanation from former England bowling coach Troy Cooley:

• "Reverse swing is all to do with the deterioration of the ball and the seam position in flight. As the ball becomes rougher, it will take on a different characteristic as it deteriorates. So if you present the ball as an outswinger, the ball has deteriorated so much on the rough side that it takes on the characteristics of the shiny side. Which means a natural outswinger will become an inswinger and conversely, an inswinger into an outswinger."

The defining point of swing is the separation point of the initial layer of air with the ball, whichever side has greater air coverage will have more lift and lower pressure, lifting and sucking the ball towards it. For greater detail on what causes separation-point differences see swing bowling.

When does the ball start to reverse?

Since reverse swing favors the older ball, it will usually start to move around the 40-over mark. However, England's bowlers during the 2005 Ashes were able to make the ball reverse after just 15 to 20 overs. Brett Lee found his reverse swing in Adelaide on the 30-over mark.

Also during the 2009 T20 World Cup Pakistani fast bowler Umar Gul managed to get reverse swing after just 11 overs.

Zaheer Khan and Lasith Malinga is a specialist of reverse swinging yorkers at the present.

But how can bowlers manage to do this so early in the innings? The most important factor to consider is the pitch. The Indian sub-continent pitches are rougher and dustier than pitches elsewhere in the world. Hence, Indian sub-continent bowlers obtain reverse-swing after 5-over mark also. In Australia and New Zealand, pitches offer no or very little help and it all depends upon how the ball is variously played. South Africa presents the same picture, where the reverse-swing is seen little or none at all. England, however has seen some change in pitch conditions in the last decade and bowlers use that to reverse their deliveries earlier.

Like footballs, each manufacturer's cricket balls are different. Some have more pronounced seams while others deteriorate slower, both of which have an influence on how the ball will move in the air.