Demystifying reverse swing

Why is everyone talking about reverse swing these days as if it's a new discovery? Sure, the English bowlers have finally learned how to do it, but seriously, it's old hat by now. Wasim and Waqar were past masters at it and it was picked up by several other bowlers in the early nineties.

Bowlers with slingier more side on actions usually generate more reverse than the high-arm, hit-the-deck-hard bowlers like Harmison. A lot of cricket websites have come up with their explanations for the phenomenon, but I've found most of them either flawed or unsatisfactory. So here's my shot at it-

For traditional swing, one side of the cricket ball is kept polished and smooth while the other side is allowed to get rough through the course of play. Once there is enough of a difference in smoothness between the two sides of the ball (which happens almost as soon as the innings begins), it is ready to swing. For outswing to the right-hander, the ball is delivered with the rough side facing left and the seam vertical (or sometimes slighty tilted towards first or second slip). During the delivery, air travels faster over the smooth side of the ball and faces more resistance from the rough side. As a result, it gets pulled in the direction in which the rough side is facing - in this case away from the batsman. For inswing, the rough side faces right and the seam is either vertical or tilted slightly to the right, towards a possible leg slip.

Once the ball gets a little older - say about 35-40 overs old, the smooth side inevitably gets rougher and stops swinging in the conventional fashion. To counter this, bowlers make sure that the initial rough side is kept as dry as possible and the smooth side as moist as possible. The smooth side is now heavier than the rough side because of all the moisture and when the ball is delivered with the rough side facing left, like a traditional outswinger, the heavier weight of the smooth side pulls the ball in its directions, i.e. into the batsman. Hence the name 'reverse swing'. The same thing can be done to get reverse outswing with a traditional inswinger's grip.

What is interesting with this English team in the Ashes is that they've managed to start getting reverse swing from the 15th over and not the 40th over when most other bowlers get it to work. No one's too sure how that's happening, but one of the plausible theories is that a different make of cricket ball is being used here and that's behaving differenty from the usual kookaburra. Hopefully we'll have a more scientific explanation by the end of the series.