Why some ball tampering offences are more serious than others

Although they can polish the ball, they are not allowed to scuff it. Scuffing the ball has a similar effect to polishing it – it will deviate in the air, making things difficult for the batsman.

Why are the players permitted to polish the ball, but not to scuff it?

Arbitrary distinctions and rules

The distinction between different ways of altering the ball, some allowed and some not, is as arbitrary as the convention that cricket should be played with 11 players rather than 10.

Ultimately, there is no rhyme or reason for either convention.

But, rightly or wrongly, they are the rules.

Introducing a "foreign object"

A convention has developed where players may use sweat or saliva to help polish the ball. But if the saliva is altered (ie through mints – think Marcus Trescothick, 2005 Ashes and Murray Mints), or if players are using hair gel, lip balm or sunscreen to polish the ball, then that crosses the line into ball tampering.

Using foreign objects to treat the cricket ball is prohibited on the basis that nothing extraneous to the game should be introduced to it. On this basis, a foreign object is not like the use of teeth, saliva, or fingernails on the ball.

Players are normally allowed to use the materials available to them in the course of the game – but only to shine the ball. Teeth and finger nails, though not extraneous to the game, are used to scuff the ball rather than polish it. But scuffing is (rightly or wrongly) illegal. Dirt – likewise not extraneous to the game – is also used not to shine but to scuff the ball. Saliva, by contrast, is used to shine the ball. Since shining is allowed, the use of saliva is permitted as it is not extraneous to the game.

One reason why Du Plessis's conduct in 2016, though illegal, was not thought as serious as Steve Smith's or Afridi's (in 2010), is that Du Plessis was using a foreign object to do what he was already allowed to do without the use of a foreign object: polish the ball. In Bancroft's case, there is a double transgression: he used a foreign object (the use of sandpaper), and he scuffed the ball, and both are illegal.

In Afridi's case, although no foreign object was involved, he did alter the ball illegally, because the objective in biting the ball is to scuff the ball up. The difference between Afridi and Du Plessis is that Du Plessis thought that he was bending but not breaking the rules, whereas Afridi would have known that scuffing the ball (by biting at the seam) was breaking the rules.

Premeditated cheating

The outrage surrounding the current Australian team's ball tampering stems from an additional layer. It is the deliberate pre-meditated cheating, and a failure to come fully clean, which has shocked the world.