The Dark Art and the Law

We end where the whole series has quietly been pointing. Every legal thing a fielding side does to the ball is about managing its two sides: polish one, let the other roughen, keep the asymmetry that makes it swing. Tampering is simply crossing one line — from maintaining that asymmetry to manufacturing it with help you're not allowed to use. The physics on both sides of the line is identical. That's what makes this the hardest rule in cricket to police, and the easiest to turn into a scandal.

What the law actually allows#

The governing rule is Law 41.3, on changing the condition of the ball, and it draws a surprisingly narrow line.

Allowed: you may polish the ball on your clothing using sweat — the origin of the red stain down every quick bowler's trousers — provided no artificial substance is involved. You may dry a wet ball with a towel, and remove mud, both under the umpires' supervision. That's essentially it.

Not allowed: rubbing the ball on the ground; using fingernails, sandpaper, bottle tops, zips or any foreign object to scratch or gouge a side; lifting or picking at the seam or the quarter seam; and applying any artificial substance — which now includes saliva, of which more in a moment. When Mehta was summoned to Lord's to advise on the issue, the methods he was shown were exactly these: gouging with bottle tops, and prising the quarter seam open with a nail.

Break the law and the umpires may change the ball, award five penalty runs to the batting side, and report the captain; the ICC's code of conduct then adds demerit points, fines and bans by severity.

The grey in the middle#

The trouble is that the line is cleaner in the law book than on the field. Mehta pointed at the genuinely awkward part: “positive roughness” — grit and dirt pressed into the surface with a bit of sweat — can help a ball reverse, and, in his words, “the evidence is gone by the time the ball reaches the wicketkeeper.” A skill whose legal and illegal versions look identical, and whose traces vanish within seconds, is a skill destined to live under permanent suspicion. It is precisely why reverse swing spent twenty years shadowed by the accusation we met in Part 7.

Four times it boiled over#

The history of tampering is a series of flashpoints, each testing where the line sits.

In 1994, England's captain Michael Atherton was caught with dirt in his pocket, applying it to the ball — the affair that prompted Mehta's summons to Lord's. In 2006 at The Oval, Pakistan were penalised for alleged tampering and refused to retake the field in protest, producing the first forfeited Test in the game's history. South Africa's Faf du Plessis was found guilty twice — in 2013 for shining the ball on a mint in his mouth, in 2016 for using the zip of his trousers.

And then, in 2018, the flagship case. In the third Test against South Africa at Newlands, Australia's Cameron Bancroft was filmed rubbing the ball with an abrasive and hiding it down his trousers — first claiming it was tape and grit, then, after his board's investigation, admitting to sandpaper. The revealing detail is that the umpires inspected the ball and neither changed it nor awarded five runs: the on-field offence was minor, the ball barely altered. Yet the scandal — a Test side caught cheating on camera — dwarfed the physical act entirely. The ICC handed Steve Smith a one-Test ban; Cricket Australia went vastly further, banning Smith and David Warner for twelve months and Bancroft for nine, with Warner judged the architect and the coach resigning. South Africa won the Test by 322 runs and the series 3–1. Many in the game — du Plessis, Shane Warne, Michael Vaughan — thought the bans wildly disproportionate to scratching a ball. It became a case less about aerodynamics than about the spirit of the game versus the letter of the law.

The line moves: saliva and a pandemic#

Which brings us to the strangest recent twist, and a fitting place to end, because it folds the whole series back on itself.

Bowlers have long believed saliva — especially sweetened by mints or sugar — is a better polishing agent than sweat, helping keep one side glassy for conventional swing and preserving the shine contrast that reverse needs. Then, in May 2020, the pandemic banned it: the ICC prohibited applying saliva to the ball as a Covid health measure, sweat still permitted. In September 2022 the ban was made permanent — and the reason is the point. The MCC's own research had concluded that shining with saliva had “little or no impact” on how much the ball swung.

But belief dies hard, exactly as Part 5 warned. In 2025 the split reopened: the Indian board lifted the saliva ban for the IPL after its captains argued the ban had killed reverse swing and tilted the game too far toward batting, while at international level the ICC kept the saliva ban but dropped the automatic ball-change that used to follow it — umpires now judge by the ball's condition, changing it only if that condition was actually altered, with five penalty runs if so. Mohammed Shami spoke for the bowlers: “we keep appealing that we should be allowed to use saliva so that we can bring reverse swing back into the game and it becomes interesting.”

“We keep appealing that we should be allowed to use saliva, so that we can bring reverse swing back into the game.” — Mohammed Shami

And there, in one argument, is everything this series has been about. On one side, the players' deep, lived conviction about what makes the ball move. On the other, the measurements, which say the effect is small — the same gap we found with the cloudy sky in Part 5. Both sides are arguing in good faith. Neither is entirely right.

That's the honest last word on swing. It is real physics — a thin layer of air, a stitched ridge, two sides of a ball made deliberately unalike — clean enough to draw in a wind tunnel. And it is also folklore, craft, suspicion and belief, none of which the physics quite dislodges. The ball still curves through the air with nothing touching it. We just understand, at last, a little of how — and argue, still, about the rest.