Cricket Ball Swing: Why a Cricket Ball Swings?

by Shiwani Pandey September 11, 2022

Understanding the Science Behind Cricket Ball Swing

Can you say what is a cricket ball made out of? Do you know how a ball can be made to swing in a particular direction and what factors are responsible for it? For people who don’t play cricket as much, it is pretty much a simple bat-and-ball game. However, aficionados who know cricket see this game as something that is a combination of basic mechanics plus strategy. On every single delivery, the ball can get a different trajectory based on the length, line, pace, and swing of the ball. 


A Bowler Swinging his Ball towards the Batsman


A Bowler Swinging his Ball towards the Batsman


It was the former fast bowler of Pakistan, Imran Khan who first introduced the concept of ‘reverse swing’ of the ball in 1977. It was pretty much a surprise for everyone given that there were many accusations made for ball-tampering and whatnot. But why did no one understand the science behind the cricket ball swing or the ‘reverse swing’ technique until much later when scientists studied it thoroughly? In this blog, we are going to talk about the ball swinging in cricket and why it takes place. 


Understand the Concept of Cricket Ball Swing Physics 

Mainly, there are 2 different things that end up swinging a ball in a particular direction. One would be the surface that the ball has and the other is the exact speed of the bowling. Rabindra Mehta, a scientist responsible for studying the cricket ball swing explained it using the concepts of fluid mechanics. When the ball is properly flying through the air, there is a thin layer of air forming along the surface of the ball called the ‘boundary layer’.

 

The boundary layer isn’t necessarily attached to the surface of the ball but is all the way around and is separated. The exact location of this point of separation will determine the correct pressure on the ball. There is a relatively late separation which results in lower pressure on that particular side. The side force or the swing will only be created if the pressure difference is intact between the 2 sides of the ball. Moreover, the point of separation for the boundary layer is actually determined by the ball’s surface and the speed of the blowing. Before getting into more details on how to swing a cricket ball, let us first know about the ball’s surface. This is where the concepts of laminar flow and turbulent flow come into action. 


When the match is beginning, the ball is shiny and smooth on both ends across the seam. However, after some time, one side of the ball becomes a bit rougher. So, the surfaces of the ball are different and the boundary layer separation of air happens in two different manners. While there is no resistance to air in the smooth layers, the other rougher layer has a disturbance. This is why the smooth layer has a laminar flow and the rough layer has a turbulent flow which results in the late separation. This difference in the flow will cause a change in the separation air speed from both sides and the ball will swing. 


Connection Between the Seam of the Ball and Swing Bowling

The ball’s seam is judiciously used by the fast bowlers in order to create the swing in the bowling. If you are wondering how that happens, it is basically with the same logic that has been explained above. The ball’s seam is basically used as the rough surface and creates a flow that is turbulent in nature which causes the ball to swing. This is basically done by efficiently releasing the ball with the seam and that too at a particular angle to the initial flight line. So, in the direction in which the seam is pointing, the ball will swing in the same direction.  So, in case the ball is released with the seam angled towards the slip fielders, it will properly swing away from the batsman. However, if the ball is released with the seam pointing towards the fine leg, it will swing right into the batsman. These cases are what we call an outswinger and an inswinger respectively. 


This is how to make a cricket ball swing even during the early overs in the match when both the sides of the ball are smooth and shiny. As more time goes on in the match, the bowlers actually try and keep one side of the ball shiny. You might have seen some bowlers apply saliva or sweat on the ball and then properly rub it against their clothes. That is done so that one side of the ball is shiny and smooth. While some people believe that the ball properly swings because it tends to lose some weight, that is not true for sure. 


How Does Reverse Swing Work? 

So, now that you know how the ball swings and how it is important to keep one side of the ball shiny, do you think that swinging is not possible after 30 overs when both sides of the ball are rough? Well, this is when the ‘reverse swing’ technique can help. As it is implied by the name, in reverse swinging, the ball will veer towards the smoother side instead of the rougher side. The efforts of the bowlers to keep a single side smooth results in the creation of one rough and another super-rough side when more than 30 overs are completed in the match. This is the time for reverse swing. In a reverse swing, the bowler might be bowling an inswinger but it will still swing away from the batsman. 


This is due to the fact that the ball’s velocity actually causes the air on both ends to transition from a turbulent to a non-turbulent flow. This flow is amplified by the rougher surface. Hence, the turbulence isn’t able to hold on to the surface and hence there is an early separation. So, the air on the turbulent layer of the comparatively smoother side will stick a bit longer before actually separating and hence the reverse swing takes place. This can be a tough challenge for the batsman because it is a tricky ball to conquer. 


Conclusion 

We hope that you enjoyed learning what is swing in cricket and how the process works. When it comes to swing blowing, the technique is surely impeccable and poses a lot of challenges for the batsman to bat. If you liked reading the blog, check out the blog section on our official website for more of such interesting topics.