What is the law around ball-tampering?
The only action which may be applied to a cricket ball is polishing without the use of an artificial substance, drying with a towel or removing mud under supervision by the umpires. Anything else is illegal.
How do cricketers tamper with the ball?
There is a long tradition of fielding sides attempting to subvert this law by manipulating the ball with outside agents - and a continuum of offences.
At the lowest end, players can use spit or sweat to polish one side of a ball and will often often suck sugary sweets or apply lip balm to aid this process. There is also a habit of throwing the ball into the wicket-keeper so one side lands on a rough, hard surface,...