Cricket: Science is all very well but swing's the thing

James Anderson. Photo / Getty Images

Contrary to some things in life being easier said than done, reverse swing is hard to explain - Nasa scientists have even been called on in the past - as well as difficult to do.

A cricket ball starts to swing in the opposite direction to convention after as few as 20 overs, depending on how early it gets roughed up. One over the ball can be moving in the direction of the seam and the rough side; after a few more it is beginning to move back the other way.

In other words, the ball swings in the opposite direction to that which the batsman expects - which can be a devastating development for a batting side and which has gained much prominence as a one-day weapon.

The concept came about in Pakistan in the late 1970s. It was a way fast bowlers could get some advantage out of their abrasive grounds and pitches when the shine on the ball did not last long. The art was passed down from Sarfraz Nawaz to Imran Khan to Wasim Akram and Waqar Younis until eventually, in an era of modern technology, the world got hold of it.

It is now common in the modern game, notably helping England to win the recent Ashes series.

For some - like the New Zealand batsmen against Pakistan in the early 1990s - it must feel like the ball is delivered under a spell but the concept does have scientific logic.

With a newish ball, the air goes over the shinier side and has more drag on the rougher side - so the ball moves in the rougher side's direction. Presuming variables like wrist positions are correct, reverse swing comes into play when the shiny side is more resistant to the air on an older ball (ie the lacquer is blemished).

Hence when bowled fast, the ( rougher) seam of the older ball traps the air and causes it to move late in the direction of the shinier side. The ball is effectively sucked into an area of less pressure.

The compulsory change to a cleaner white ball after 35 overs means, if reverse swing has been utilised between overs 20-34, it is difficult to implement again until the final five overs. That takes a significant weapon away from the bowling team.

Despite the World Cup being on the sub-continent, even those grounds are more lush than in the past, meaning it takes longer for the ball to deteriorate. That is where dodgy tactics like deliberate scuffing via bounce throws (with the rough side skimming the ground), hair gel, mints or bottle tops in the pocket come into play rather than using basic sweat and saliva.

Across-the-seam bowling can also work, roughing the ball quicker. Umpires need to be wary of tactics like spin bowlers drying sweaty hands on the pitch, but retaining a little bit of dirt to work into the ball; to provoke reverse swing.

Former New Zealand pace bowler Danny Morrison remembers one ingenious opponent's trick: "He had a band aid on his finger but one part of it was a piece of sandpaper; that way he ended up with one side of the ball like felt and another side smooth - outrageous," he laughs.

Morrison also stresses other elements need to be choreographed into a decent reverse swing performance.

"You need a strong wrist positioned expertly like James Anderson's; right behind the ball to steer it.

"Hiding the ball helps, too. Guys run in holding it in both hands so you cannot see the rough and shiny sides. Wasim [Akram] did that well. That's where an eagle-eyed non-striker can help. If he watches the bowler carefully, he can put his bat in his left or right hand indicating to the striker whether he thinks it will be an in or out-swinger."

Black Caps bowlers have been trying to master reverse swing for years with Kyle Mills probably the best current exponent. Chris Cairns used to try his best and has stressed how important it will be on the sub-continent.

"Much is made of the preservation of the ball for reverse swing. While that is fundamental, the release of the ball is paramount in extracting maximum movement.

"In-swing bowlers to a right hander with the new ball, like Allan Donald and Shane Bond, were stronger at outswing with the old ball.

"Conversely, outswingers with the new ball - like Waqar and Darren Gough - lend themselves to booming inswingers with the old ball. Two great exponents of reverse were Wasim and Glenn McGrath who, because of their release position, could move the ball both ways.

"Reverse swing will play a big part in the sub-continent. It not only offers wicket-taking opportunities but stunts the run rate. Scoring inside the first 20 overs will be crucial."