What Is Reverse Swing? The Science, History and Laws

Reverse swing is swing in the opposite direction to the one the seam suggests. A bowler holding the ball with the seam angled towards the slips expects it to move away from a right-handed batter; with reverse swing, the same grip and action make it move in. It happens with an older, scuffed ball, or at very high speed, and it is hard to play because the batter reads the seam and the ball does the opposite. This page explains the science, the history, and what bowlers may and may not do to the ball to get it.

How Normal Swing Works

A cricket ball has a raised seam of six rows of stitching. When the ball is bowled with the seam at an angle, the seam disturbs the thin layer of air flowing over that side of the ball and makes it turbulent, while the air over the smooth side stays smooth, or laminar. Turbulent air clings to the ball for longer before breaking away, so the two sides of the ball break the air away at different points. The result is a sideways force, and the ball swings towards the side the seam is pointing to. The aerodynamicist Rabindra Mehta, who studied swing at NASA's Ames Research Center, found it is strongest at around 30 metres a second, about 67 mph, in his wind-tunnel tests, and that most of the movement happens in the second half of the ball's flight, which is why good swing looks late.

How Reverse Swing Works

At higher speeds, or once the ball is rough, the air on both sides of the ball becomes turbulent. The seam then works against itself: in Mehta's explanation, it thickens the turbulent layer on its own side so that the air breaks away earlier there than on the other side. The force flips, and the ball swings away from the side the seam points to. That is reverse swing. Later work at the University of Bath points to a slightly different flow feature on a match-worn ball, but both explanations agree on what the batter sees: same seam, opposite swing.

Three findings from Mehta's NASA research matter most to bowlers:

• Roughness brings it down to bowlable speeds. In his tests, a new two-piece ball only reversed above about 100 mph, a new four-piece ball above about 80 mph, and a ball used for around 100 overs from about 65 mph. He stresses that these figures were for the balls he tested, and that the real threshold depends on the seam angle, the surface, the air and the spin.
• The two sides need to be different. For conventional swing the side away from the seam should be kept as smooth as possible; for reverse swing it needs to be as rough as possible. That is why fielding sides polish one side only and let the other wear.
• No change of grip is needed. Once one side is rough enough, the bowler turns the ball over and bowls with the same grip and action, and the ball goes the other way. The batter cannot read it from the hand.

Conventional, Reverse and Contrast Swing

Mehta also tested two pieces of dressing-room wisdom. Wetting one side of the ball to make it heavier has, he found, no aerodynamic basis, and a wet ball swings less. And he found no scientific evidence that humid conditions make the ball swing more.

Who Discovered Reverse Swing

Pakistan's fast bowlers. Mehta names Imran Khan, Sarfraz Nawaz, Wasim Akram and Waqar Younis as the bowlers who first showed what it could do, and says it became widely talked about from the mid-1980s. Sarfraz is generally credited as the pioneer: he has said he learned to keep the shine on one side only through trial and error, and passed the skill to Imran, who passed it to Wasim and Waqar. Both Sarfraz and Waqar have insisted it can be achieved without tampering with the ball. England made it famous in the 2005 Ashes, when Simon Jones took 18 wickets at an average of 21, with his mastery of reverse swing described by Wisden as critical to England's success.

What Bowlers May Do to the Ball

The Laws allow fielders to polish the ball on their clothing, with sweat as the only natural substance, and to remove mud and dry the ball under the umpire's supervision. Anything else that changes the condition of the ball is an offence, punished with five penalty runs and a replacement ball. Saliva is no longer allowed under the Laws or in international cricket: it was banned during the pandemic, and the ICC made the ban permanent in October 2022. MCC said at the time that data from international cricket showed the saliva ban had made very little difference to swing, because sweat worked just as well.

The IPL is the exception. It allowed bowlers to use saliva again from the 2025 season, by an advisory after its captains' meeting, though the published IPL 2026 playing conditions still mention sweat only. Our guides cover why cricketers shine the ball, the biggest ball-tampering scandals, and the Law on unfair play.

Why Reverse Swing Is Hard to Play

Batters pick swing from the seam position in the bowler's hand. With reverse swing that cue points the wrong way, the ball is older and usually being bowled fast, and the movement comes late. Mehta's research found that most swing happens in the second half of the ball's flight whatever the type, which leaves the batter little time to adjust.

FAQs: Reverse Swing

What is reverse swing in simple terms?
Swing in the opposite direction to the way the seam is pointing, usually with an old, rough ball or at very high speed.

Why does an old ball reverse swing?
A rough surface makes the airflow turbulent at lower speeds, so reverse swing starts at speeds a fast bowler can reach. Mehta's tests put it at about 65 mph for a ball used for around 100 overs.

Can a new ball reverse swing?
In principle, if bowled fast enough. Mehta's tests put it above about 80 mph for a new four-piece ball, against about 65 mph for a ball used for around 100 overs.

Who invented reverse swing?
Pakistan's fast bowlers, with Sarfraz Nawaz generally credited as the pioneer and Imran Khan, Wasim Akram and Waqar Younis its best-known exponents.

Is it legal to use saliva on the ball?
Not under the Laws or in international cricket since 2022. The IPL allowed it from 2025.

Is reverse swing ball tampering?
No. Reverse swing is legal; illegally roughening the ball to get it is tampering.