January 29, 2017

When the new ball reverses

Rabi Mehta and Garfield Robinson
Is it reverse swing or contrast swing? There is a difference between the two, and a better understanding of it would enhance the effectiveness of the skill

Jonathan Trott is trapped leg before by Jerome Taylor with a new ball that swung in unexpectedly © Getty Images

A curious thing happened during the recent Australia-Pakistan ODI in Brisbane. In the fifth over, Mohammad Amir bowled a peach of a ball to David Warner. With the seam canted towards slip, the delivery started on the line of middle stump before swinging away, evading the left-hand batsman's attempted flick to leg by some distance, before clipping the bails. It was an exquisite, almost unplayable outswinger, behaving much as the bowler intended, and defeating a highly capable batsman in prime form.

It is the delivery that followed, however, that is more interesting, at least for the purposes of this article.

This time it was Steven Smith taking strike and facing the first ball. The ball left Amir's grip with the seam pointed in the same direction as the previous delivery, apparently intended to move in to the right-hander. It swung away instead, and Smith, walking into an off drive, edged a catch through to the wicketkeeper.

"What a delivery," remarked one Channel Nine pundit. "Totally different to what he bowled to Warner. This was going away from the right-hander, Smith… he was expecting the ball to come in." Amir had gone past Warner's bat on a few occasions with deliveries swinging away. Smith might therefore have expected the ball that got him to have behaved similarly.

In Barbados in May 2015, right-arm fast bowler Jerome Taylor was bowling the fifth over of England's second innings to Jonathan Trott. The fifth delivery was full, swung in slightly, went past the inside edge and struck the right-hander on his pads. Billy Bowden's crooked index finger shot up in response to an almighty appeal and the batsman trudged off after being dissuaded by his partner and captain, Alastair Cook, from requesting a review. Slow-motion replays clarified that though the delivery swung into the batsman, the seam was pointed in the direction of slip, hinting that the delivery ought to have swung away. Previously, Taylor had been largely swinging the ball away from Trott, so the batsman was no doubt surprised to see this one swing in.

Whenever the old ball swings, it is immediately said to be reversing. Contrast swing is rarely mentioned, and yet, that is more likely the correct characterisation

The television commentators didn't seem to be able to explain what had happened either. In the end they appeared to put it down to being just one of those things that sometimes occurred. Something similar, perhaps, to one spinning delivery turning and another going straight on - just some kind of natural variation.

But there is much that science can explain, such as the effects of the aerodynamic forces acting on a cricket ball flying through the air. For conventional swing, the ball is expected to deviate in the direction in which the seam is pointed, while for real or true reverse swing, the ball swings in a direction that is opposed to that of the seam.

Since the two deliveries under scrutiny (Taylor to Trott and Amir to Smith) unmistakably moved in opposition to the orientation of the seam, both are probably best explained by real or true reverse swing.

Now, many of us have been led to believe that the new ball does not meet the requirements necessary for reverse swing to transpire. To enable the technique, it is widely believed that the ball has to have aged at least 40 overs, with one side tended to and polished (without any external substances, of course) and the other allowed to grow rough and unkempt. That is indeed one method of facilitating it, but studies have shown that reverse swing can be, and is, achieved with the new ball as well.

One requirement for it to occur is that the bowling speed needs to be around 90mph or higher. Amir's deliveries that sent back Warner and Smith had similar seam orientation. Both were delivered at or very close to 90mph. So why did they bend in opposite directions? It is not widely known, but even with a brand new ball, there is often a subtle but noticeable difference in surface roughness between the two sides (due to differences in embossments or markings). There is a possibility also that one of the sides picked up a slight blemish even after only four overs.

The position of the seam corresponds to the direction of the swing - when the swing is conventional © Getty Images

One hypothesis is that in Warner's case the ball was probably released with the relatively smooth side facing the batsman, and in Smith's case, the ball was flipped over so that the relatively rough side was facing him. It is unlikely the bowler did this deliberately. One of the peculiarities of reverse swing is that the bowler need not alter his grip on the ball or his action. Therefore, the right-arm fast bowler who normally swings the new ball away from the right-hand batsman will often swing the old ball in without any change in bowling technique. Fidel Edwards, for instance, typically swings the new ball away, but is known to deliver searing inswingers with the old ball. Dale Steyn also mostly bowls outswing with the new ball and inswing with the old.

Often confused with reverse swing is what is properly known as contrast swing. How is it different from reverse? Contrast swing occurs when the ball is released with the seam straight up, rather than angled towards slip or leg slip. The ball will swing when there is a contrast in surface conditions between the two sides of the ball. The greater the disparity in roughness and smoothness, the greater the inclination for the ball to change direction. At the bowling speeds normally achieved by fast bowlers, say between 70 and 85mph, the ball will swing towards the smooth or shiny side.

Indian fast bowler Mohammed Shami consistently bowls with the seam straight up (contrast mode), and normally operates at speeds of up to 85mph (close to 140kph). ESPNcricinfo's match report from Shami's Test debut, against West Indies in 2013, says: "Shami bowled consistently in the late 130s on a slow pitch, and was a different proposition with the ball scuffed up, finding movement that had not been there for him with the new one."

The movement was noticeable only when Shami returned to the attack in the 42nd over. Unsurprisingly, it was referred to as reverse rather than contrast swing at the time.

So are there any advantages of contrast swing over reverse swing?

One, it is much easier for non-swing bowlers to release the ball with the seam straight up rather than angled. Contrast swing is also possible with the seam completely bashed in - a common occurrence in the subcontinent. A prominent seam plays a critical role in conventional and reverse swing. Whenever the old ball swings, it is immediately said to be reversing. Contrast swing is rarely mentioned, and yet, that is more likely the correct characterisation. What we have seen, more often than not, is that both contrast and reverse swing are lumped together and labelled reverse.

Can a brand new ball achieve contrast swing? If both sides of a new ball are in similar condition, it follows that there will be no contrast swing.

But, as we pointed out above for the reverse cases, if there is a slight difference due to different embossments, or one side picks up a blemish, even a slight one, then there is a chance for contrast swing. And since the difference in roughness will be relatively small, it will only occur at the higher speeds, say around 90mph or higher.

It is possible to identify the type of swing a bowler is producing by making note of the positioning of the seam and the direction of the swing. If they are coincident, then it is conventional swing; if opposed, it is reverse swing; and if the seam is pointing straight down the pitch, then rest assured that you have just observed contrast swing.

Swing is one of the fast bowler's most important weapons. Increased knowledge of its workings and scientific underpinnings should not only lead to a better understanding of the skills on display but also enhance our appreciation of the nuances of the great game.

Rabi Mehta is a sports aerodynamics consultant in California. Garfield Robinson is a freelance cricket writer @spiider10

Comments have now been closed for this article

  • thomas on January 31, 2017, 9:15 GMT

    This is interesting for me as not being one of the team's top bowlers I often had to practice with an OLD ball - no shine whatsoever and very little seam, so we had to make it shiny using sweat. I also learned my cricket in Denmark, and at least in my club, no one seemed to know what conventional swing was. You swung the ball by polishing one side (even when the ball was new), and by modifying your action. While you always held the seam upright, if you wanted to bowl an inswinger (right arm bowler to right hand batsman), you also had to make sure that your arm was VERY upright at the time of release, almost pointing towards one o'clock. If you wanted to bowl an outwinger, the arm would be pointing towards eleven o'clock at the time of release. So the ball swung with the shine, but also with the arm. When the ball was new, getting the action right was most important, when the ball was older, ball alignment and action had to be right. And it worked, even for a slower bowler like me.

  • Muhammad Ali on January 31, 2017, 7:02 GMT

    Waqar Younis used to reverse swing new ball as well. Sometimes, the seam acts as abrasive side to the shiny side and that can create one shiny while other rough side to generate reverse swing.

  • Tony on January 30, 2017, 16:14 GMT

    This may be spot on scientifically but as far as making a young bowler a swing demon one should be cautious. If it was that easy by pointing the seam and ensuring the shiny side was in the direction you wanted it to swing and then switching one ball would swing in and the next one out. It doesn't work as there are so many other variables. Rt hand bowlers with open chested actions tend to move the ball into a rt handed batter and with a closed action away. Wind direction, humidity make of ball (different seam heights) different balls from the same box all have an affect. Different bowlers have different natural characteristics which may or may not benefit from science. Give me youngster with complete control of length and line and the ability to adjust depending on who they are bowling to as opposed to one who swings the ball and has no idea where it is going.

  • bendzi2952098 on January 30, 2017, 13:40 GMT

    The article does a good job of making things sound more confusing then it needs to. A simple summary is that there are 2 primary aerodynamic causes for a ball to swing:

    1. The seam orientation and overall geometry of the ball. This is what leads a ball to (conventionally) swing in the direction that the seam is pointed.

    2. The contrast in surface roughness on each side of the ball. Assuming the seam to be held perfectly straight, the ball will swing towards the smoother side. The greater the difference in smoothness between sides, the greater the degree of swing.

    The definition of "reverse" and "contrast" swing as above is purely academic and makes no difference on the cricket pitch. For the player, the ball is said to "reverse" when it moves in the opposite direction than it would otherwise be expected. The simplest example of this is when the "swing force" from the roughness difference overcomes the "swing force" from the seam orientation.

  • kallappa on January 30, 2017, 10:59 GMT

    every article talks on rough side and smooth side for swing, but my unanswered question is how a bowler can bowl both with a new ball (first over, first 2 balls). both the sides are smooth right?

  • Kiran on January 30, 2017, 9:20 GMT

    Good explanation.Adding on,for the ball to swing,there should be some back spin induced along with a proper seam position.Also,the numbers given for the threshold speeds changes with the balls used.In the case of SG balls used in India we will more often experience contrast swing than the reverse.The reason for this being,contrast doesn't need a perfect seam position(could be scramble aslo) but the scruffiness and high speeds(defined by the conditions,mostly >140kph).The best example for this would be Dale Steyn spell in Nagpur.Since the polish and seam of SG balls are poor it's very difficult to swing this ball conventionally when the conditions are relatively hot.Reason for this could be that the back spin won't be induced which generally comes because of the action and release for a good stitched seam ball.So,Ideally we should have lumped conventional and reverse swing in one category and contrast swing to something special.

  • Jacob on January 29, 2017, 18:35 GMT

    It appears like the 'physics' behind reverse and contrast swings is nearly similar.

    Am I right to say that a swinging ball with an upright seam constitutes contrast swing?

  • Arvin on January 29, 2017, 12:18 GMT

    Dr. Mehta, Mr. Robinsson Thank you for clarifying on this issue once again. But one thing which is not part of your analysis and wind tunnel experiments is the issue of wrist position and how you apply force at the time of release. Could that affect the swing. Wasim Akram always bring that up. Now I am sure we cannot take his word, he only practiced swing bowling. Second, is there any chaotic behavior in this phenomenon that can given a different explanation for 'reverse swing' like observations with the new ball.

  • Andrew on January 29, 2017, 7:35 GMT

    It is with interest that I read this article and the comments. I've never flown a plane or sailed a yacht but I do understand dynamics and aerodynamic "lift" which is what makes a plane fly and a yacht sail. This same "lift" principal is what makes a cricket ball swing. In laymans speak lift is produced by air having to travel at different speeds across two connected surfaces. Simply if the air has to travel further, hence faster, on one surface there is a loss of pressure and the object will move to this lower pressure area. So depending on the respective roughness of the surfaces (or not), and how pronounced the seam is, there are different swing directions available with very subtle changes in seam orientation/angle of delivery. That said I also believe that no 2 balls are identical and the centre of gravity is very unlikely to be exactly in the centre of the ball. Have you noticed how some balls swing alot and some don't. If the centre of gravity is off centre it will swing more.

  • rob on January 29, 2017, 5:17 GMT

    I wish I had read this article 20 years ago when I was playing. I was in the team as a swing bowler but I didn't really understand what was going on. I simply pointed the seam one way of the other and hoped for the best. It never occurred to me to try the vertical seam trick. If I had know I would certainly have tried it. Better batsmen can see which way the seam is pointed fairly early but I doubt too many would know which side of the ball had the most writing on it. That would be the bowlers little secret.

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