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Science

The Do’s and Don’ts of Ball-Tampering

28 May 2018

“A big mistake,” protested the team captain. “Contrary to the spirit of the game,” intoned the umpires. “A shocking
disappointment,” quoth no less a personage than the prime minister himself.

Really—it’s just not cricket.

But cricket it was, and for two weeks mass media could not tear their eyes from it. A junior Aussie bowler, baggy green snug over his brow, facing down the intransigent Proteas on a blistering South African afternoon, and—desperate to outfox his foe with a curly delivery—vigorously scuffing up one side of a cricket ball with a bit of yellow sandpaper.

It was a disgrace to the sport, and none-too-salutary a moment for the gormless Cameron Bancroft either, who—in a legendary bid to close the gate after the horse had bolted— proceeded to shove the incriminating implements right down his tighty-whities wherefore to continue the apparently vital business of polishing his round one.

Ball-tampering. It’s a dastardly, unsportsmanlike deed. And, to add insult to injury—it doesn’t actually work.

To understand why, we need to go back to the basics.

Cricket is a game where one team takes it in turns to try and knock over a pile of sticks (the wickets) with a shiny red leather ball, while the other team takes it in turns to defend said pile of sticks (the wickets) with a big fat stick (the bat), and also do some shuttle runs for extra cardio. The teams swap roles a couple of times and after about five days of exhausting spectacle they either call it a draw or someone gives up. This is cricket as it is played.

You would be forgiven for thinking it sounds dull. This columnist, at least, will forgive you—this columnist’s sports- mad spouse will not. Far from dull, a good game of test cricket is a tense affair of wits, wills, weather and wonky physics.

In a game of cricket, the bowler and the batter are separated by 22 yards of hard-packed grass—the “pitch”. It’s a long way to throw a ball, so bowlers are permitted one bounce on their way to wiping out the wickets. Over the multiple days of a hard-fought match, the pitch can begin to develop cracks and crevices. If the ball hits one of these, it can bounce wildly, taking the batter by surprise.

But contact with a coarse pitch can put wear and tear on the ball too—and this is where the real magic happens.

Unlike most sports balls, cricket balls are not perfect spheres: they bulge at the equator, like the Earth. This equator—the raised seam that stitches its two leather faces together—has all sorts of effects on the flight of the ball. For starters, it creates a rotational symmetry that keeps the ball spinning parallel to the seam (in an “east–west” sense) rather than perpendicular to it (a “north–south” sense).

Because spin is actually a kind of acceleration (freaky but true), you have to do work to change the axis of rotation. This is the same force that keeps frisbees from flipping over in flight. Essentially, the seam of a cricket ball allows the bowler to choose which direction the ball is facing as it flies through the air—and which side hits the ground first.

Think about what that means. A good bowler can deliberately make the ball rougher on one side than the other. Better yet, they can choose which direction the rough side faces when the ball is in motion. The rough side creates turbulence in the air that “sucks” the ball toward it—what cricketers call “swing”. A good bowler can even enhance this effect by placing the seam so that it breaks the flow of air over the ball, or splits it evenly down the middle.

So in a sense, ball-tampering in cricket is not only not illegal—it’s the heart and soul of the game. But it has to happen fairly, by repeated contact with the pitch, the bat and maybe the bowler’s trousers—not at the hands of an idiot with a lurid scrap of sandpaper.

If the weather does not cooperate, the pitch will stay fresh and firm, the ball will remain smooth and shiny, and the batters will find it all-too-easy to dispatch the bowler’s best efforts with impunity. And this is exactly what happened to the beleaguered Australians during that test against South Africa.

In the end, Bancroft’s actions were not only against the rules: they were also ineffectual. After all, two minutes of furtive rubbing can hardly be expected to deliver the same result as hours of prolonged contact, as the 25-year-old ought to have learned (on and off the cricket pitch) long ago. After a brief consultation, umpires judged his ball-tampering efforts to be laughable, play resumed, South Africa belted home, and the green-and-gold went on to lose the test by a humiliating 322 runs.

And that is cricket.


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